 Chapter 36 of Principle of Geology This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org Recording by Emanuela Principle of Geology by Charles Lille Whether species have a real existence in nature? Continued Phenomena of hybrids Hunters' opinions Mews not strictly intermediate between parent species Hybrid plants Experiments of curroiter and big man Vegetable hybrids prolific throughout several generations Why rare in a wild state? Ducandol on hybrid plants Phenomena of hybrids confirm the distinctness of species Theory of degradation in the intelligence of animals as indicated by the facial angle Doctrine that certain organs of the fetus in mammalia assume successively the form of fish, reptile and bird Recapitulation Phenomena of hybrids We have yet to consider another class of phenomena, those relating to the production of hybrids, which have been regarded in a very different light with reference to their bearing to the question of the permanent distinctness of species Some naturalists considering them as affording the strongest of all proofs in favor of the reality of species Others, on the contrary, appealing to them as contensing the opposite doctrine That all the varieties of organization and instinct now exhibited in the animal and vegetable kingdoms may have been propagated from a small number of original types In regard to the mammals and birds, it is found that no sexual union will take place between races which are removed from each other in the habits and organization and it is only in species that are very nearly allied that such unions produce offspring It may be laid down as a general rule, admitting or very few exceptions among quadruplets that the hybrid progeny is sterile and there seem to be no well authenticated examples of the continuance of the new race beyond one generation The principal number of observations and experiments relate to the mix of springs of the horse and the ass And in this case it is well established that the humule can generate and the humule produce Such cases occur in Spain and Italy and much more frequently in the West Indies and New Holland But these mules have never bred in cold climates, seldom in warm regions and still more rarely in temperate countries The hybrid offspring of the she-ass and stallion, the hinnosh of Aristotle and the hinnos of Guinea differs from the mule or the offsprings of the ass and mare In both cases, says Buffon, these animals retain more of the dam than of the sire not only in the magnitude, but in the figure of the body Whereas in the form of the head, limbs and tail, they bear a greater resemblance to the sire The same naturalist infers from various experiments respecting crossbreeds between the higote and the you The dog and she-wolf, the goldfinch and cannery bird, that the mare transmits his sex to the greatest number and that the preponderance of males over females exceeds that which prevails where the parents are of the same species Hunters' Opinion The celebrated John Hunter has observed that the true distinction of species must ultimately be gathered from their incapacity of propagating with each other and producing offspring capable of again continuing itself He was unwilling, however, to admit that the horse and the ass were of the same species because some rare instances had been adduced of the breeding of mews although he maintained that the wolf, the dog and the jackal were all of one species because he had found, by two experiments, that the dog would breed both with the wolf and the jackal and that the mule, in each case, would breed again with the dog In these cases, however, it may be observed that there was always one parent at least of pure breeds and no proof was obtained that the true hybrid race could be perpetuated A fact of which, I believe, no examples are yet recorded, either in regard to mixtures of the horse and the ass or any other of the mammalia Should the fact be hereafter ascertained that two mews can propagate their kind we must still enquire whether the offspring may not be regarded in the light of a monstrous birth proceeding from some accidental cause or, rather, to speak more philosophically from some general law not yet understood but which may not be permitted permanently to interfere with those glows of generation by which species may, in general, be prevented from becoming blended If, for example, we discovered that the progeny of a mule race degenerated greatly in the first generation in force, sagacity or any attribute necessary for its preservation in a state of nature we might infer that, like a monster, it is a mere temporary and fortuitous variety nor does it seem probable that the greater number of such monsters could ever occur unless obtained by art For, in Hunter's experiments, stratagem or force was, in most instances, employed to bring about the irregular connection Mules not strictly intermediate between the parent species It seems rarely to happen that the mule offspring is truly intermediating character between the two parents Thus, Hunter mentions that, in his experiments, one of the hybrid poops resembled the wolf much more than the rest of the litter and we are informed by Wigman that, in a litter lately obtained in the Royal Menagerie at Berlin from a white pointer and the she-wolf, two of the cubs resembled the common wolf dog but the third was like a pointer with a hanging ears There is, undoubtedly, a very close analogy between this phenomena and those presented by the intermixture of distant races of the same species both in the inferior animals and in men Dr. Pritchard, in his Physical History of Mankind, cites examples where the peculiarities of the parents have been transmitted very equally to the offspring as were children entirely white or perfectly black have sprung from the union of the European and the Negro Sometimes, the color or other peculiarities of one parent, after having failed to show themselves in the immediate progeny reappear in a subsequent generation, as were a white child is born of two black parents, the grandfather having been a white The same author judiciously observes that, if different species mix at their breed and hybrid races were often propagated the animal world would soon present a scene of confusion its tribes would be everywhere blended together and we should perhaps find more hybrid creatures than genuine and uncorrupted races Hybrid Plants Cal-Reuters Experiments The history of the Vegetable Kingdom has been thought to afford more decisive evidence in favor of the theory of the formation of new and permanent species from hybrid stocks The first accurate experiments in illustration of this curious subject appear to have been made by Cal-Reuters who obtain a hybrid from two species of tobacco, Nicoziana Rustica and Nicoziana Paniculata which differ greatly in the shape of their leaves, the color of the Corolla and the height of the stem The stigma of a plant of Nicoziana Rustica was impregnated with the pollen of a plant of Nicoziana Paniculata The seed ripened and produced a hybrid which was intermediate between the two parents and which, like all the hybrids which this botanist brought up, had imperfect stamings He afterwards impregnated this hybrid with the pollen of Nicoziana Paniculata and obtained plants which much more resembled the last This he continued through several generations until, by super severance, he actually changed the Nicoziana Rustica into the Nicoziana Paniculata The plan of impregnation adopted was the cutting off of the enters of the plant intended for fructification before they had shed pollen and then laying on foreign pollen upon the stigma Wickman's experiments The same experiment has since been repeated with success by Wickman, who found that he could bring back the hybrids to the exact likeness of their parent by crossing them a sufficient number of times The blending of the characters of the parent's stalks in many other of Wickman's experiments was complete The color and shape of the leaves and flowers and even the scent being intermediate as in the offspring of the two species of Berbascum An intermarriage also between the common onion and the leek Allium cepa and Allium porrum gave a mule plant which, in the character of its leaves and flowers, approached most nearly to the garden onion but had the elongated bulbous root and smell of the leek The same botanist remarks that vegetable hybrids were not strictly intermediate more frequently approached the female than the male parent species but they never exhibit characters foreign to both Eric Ross, with one of the original stalks, generally causes the mule plant to revert towards that stalk but it is not always the case, the hoof spring sometimes continuing to exhibit the character of a full hybrid In general, the success attending the production and perpetuity of hybrids among plants depends, as in the animal kingdom, on the degree of proximity between the species intermarried If their organization be very remote, impregnation never takes place If somewhat less distant, seeds are formed but always imperfect and sterile The next degree of relationship yields hybrid seedings but these are barren And it is only when the parent species are very nearly allied that the hybrid race may be perpetuated for several generations Even in this case the best authenticated examples seem confined to the crossing of hybrids with the individuals of pure breed In none of the experiments most accurately detailed does it appear that both the parents were mules Wigman diversified as much as possible his model bringing about these irregular unions among plants He often sowed parallel rows near to each other of the species from which he desired to breed And instead of mutilating, after coroiter's fashion, the plants of one of the parent's stalks, he merely washed the pollen off their anthers The branches of the plants in each row were then gently bent towards each other and intertwined So that the wind and numerous insects as they passed from the flowers of one to those of the other species carried the pollen and produced fecundation Predictable hybrids were rare in a while slate The same observer saw a good simplification of the manner in which hybrids may be formed in a state of nature Some wall flowers and pinks had been growing in a garden in a dry sunny situation and their stigmas had been ripened so as to be moist and to absorb pollen with avidity, although the anthers were not yet developed These stigmas became impregnated by pollen blown from some other addition plants of the same species but had they been of different species and not too remote in the organization, mule races must have resulted When, indeed, we consider how busily some insects have been shown to be engaged in conveying anther dust from flower to flower especially bees, flower-eating beetles and the like, it seems a most enigmatic problem how it can happen that promiscuous alliances between distinct species are not perpetually curing How continually do we observe the bees diligently employed in collecting the red and yellow powder by which the stigmas of flowers are covered, loading it on their hind legs and carrying it to their hive for the purpose of feeding their young In thus providing for their own progeny, these insects assist materially the process of fortification Few persons need to be reminded that the stigmas in certain plants grow on different blossoms from the pistils and unless the summit of the pistil be touched with the fertilizing dust, the fruit does not swell, nor the seed arrive at maturity It is by the help of bees chiefly that the development of the fruit of many such species is secured The powder which they have collected from the stigmas being unconsciously left by them in visiting the pistils How often, during the heat of a summer's day, do we see the maze of the issue's plants, such as the U3, standing separate from the females and sending off into the air upon the slightest breath of wind, clouds of Bojan pollen that the Zephyr should so rally intervene so fecundate the plants of one species with the unheard dust of others seems almost to realize the converse of the miracle believed by the creedless herdsmen of the Lusitanian Maze Hore omnes verse in Zephyrum, stanto rupibus altis, exceptan coeleves auras et sepesi neullis, coniugis ventogravide mirabile dictu But in the first place it appears that there is a natural version in plant as well as in animals to regular sexual unions And in most of the successful experiments in the animal and vegetable world, some violence has been used in order to procure impregnation The stigma imbibes, slowly and reluctantly, the granules of the pollen of another species, even when it is abundantly covered with it And if it happened that, during this period, ever so slightly quantity of the unheard dust of its own species allied upon it This is instantly absorbed and the effect of the foreign pollen destroyed Besides, it doesn't often happen that the male and female organs of rectification in different species arrive at the state of maturity at precisely the same time Even where such synchronisms thus prevail so that a crossing of impregnation is affected, the chances are very numerous against the establishment of a hybrid race If we consider the vegetable kingdom generally, it must be recollected that even of the seeds which are well ripened, a great part are either eaten by insects, birds and other animals Or decay for want of room and opportunity to germinate Unearthly plants are the first which are cut off by causes prejudicial to the species, being usually stifled by more vigorous individuals of their own kind If, therefore, the relative fecunity or arduousness of hybrids being the least degree inferior, they cannot maintain their footing for many generations Even if they were ever produced beyond one generation in a wise state In the universal struggle, for as extent, the right of the strongest eventually prevails And the strength and durability of race depend mainly on its prolificness, in which hybrids are acknowledged to be deficient Centauria hybrida, a plant which never bears seed, and is supposed to be produced by the fragmented mixture of two well-known species of centauria, grows wild upon a hill near Turin Ranunculus lacerus, also sterile, has been produced accidentally at Grenoble, and near Paris by the Union of Turinunculi But this occurred in gardens Mr. Herbert's experiments Mr. Herbert, in one of his ingenious papers on new plants, endeavours to account for their non-occurrence in a state of nature From the circumstance that all the combinations that were likely to occur have already been made many centuries ago And have formed the value species of botanists But in our gardens, he says, whenever species having a certain degree of affinity to each other are transported from different countries And brought, for the first time into contact, they give rise to hybrid species But we have no data as yet to warrant the conclusion that a single permanent hybrid race has ever been formed Even in gardens, by the intermarriage of two allied species brought from distant habitations Until some fact of this kind is fairly established, and a new species, capable of perpetuating itself in a state of perfect independence of man Can be pointed out, it seems reasonable to call in question entirely this hypothetical source of new species That varieties do sometimes spring up from crossbreeds in a natural way, can hardly be doubted But they probably die out even more rapidly than races propagated by graphs or layers Opinion of Ducandol Ducandol, whose opinion on a philosophical question of this kind deserves the greatest attention, has observed in his essay on botanical geography That the varieties of plants range themselves under two general heads Those produced by external circumstances, and those formed by hybridity After reducing various arguments to show that neither of these causes can explain the permanent diversity of plants indigenous in different regions He says, in regard to the crossing of races I can perfectly comprehend without altogether sharing your opinion That, where many species of the same genera occur near together, hybrid species may be formed And I am aware that the great number of species of certain genera which are found in particular region may be explained in this manner But I am unable to conceive how anyone can regard the same explanation as applicable to species which live naturally at great distances If the three larges, for example, now known in the world, lived in the same localities I might then believe that one of them was the produce of the crossing of the two others But I never could admit that the Siberian species has been produced by the crossing of those of Europe and America I see, then, that there exist in organized beings permanent differences Which cannot be referred to any one of the actual causes of variation And these differences are what constitute species Reality of species confirmed by the phenomena of hybrids The most decisive arguments, perhaps, amongst many others Against the probability of the derivation of permanent species from crossbreeds Are to be drawn from the fact alluded to by Duke and all Of species having a close affinity to each other Occuring in distinct botanical provinces or countries inhabited by groups of distinct species of indigenous plants For in this case naturalists who are not prepared to go the whole length of the transmutationists Are under the necessity of admitting that, in some cases, species which approach very near to each other In their characters were so created from their origin An admission fatter to the idea of its being a general law of nature That a few original types only should be formed And that all intermediate races should spring from the intermixture of those stocks This notion indeed is wholly at variance with all that we know of hybrid generation For the phenomena entitled last to a firm that had the types being at first somewhat distinct No crossbreeds would ever have been produced Much less those prolific races which we now recognize as distinct species In regard, moreover, to the permanent propagation of hybrid races among animals Insuperable difficulties present themselves When we endeavour to conceive the blending together of the different instincts and properties of two species So as to ensure that preservation of the intermediates race The common mule, when obtained by human art, may be protected by the power of man But in a wild state it would not have precisely the same ones either as yours or the s And if in consequence of some difference of this kind it strayed from the herd It would soon be hunted down by beasts for prey and destroyed If we take some genus of insects such as the bee We find that each of the numerous species have some difference in its habits Its mode of collecting honey or constructing its dwelling or providing for its young And other particulars In the case of the common hive bee the workers are described by Kirby and Spence As being endowed with no less than 30 distinct instincts So also, we find that amongst a most numerous class of spiders There are nearly as many different modes of spinning their webs as there are species When we recollect how complicated are the relations of these instincts with co-existing species Both of the animals and vegetable kingdoms It is scarcely possible to imagine that the bastard race could spring from the UNOV2 of this species And retain just so much of the qualities of each parent's stock As to preserve its ground in spite of the dangers which surround it We might also ask if a few generic types alone have been created among insects And the intermediate species have proceeded from hybridity Where are those original types combining as they ought to do The elements of all the instincts which have made their appearance in the numerous derivative races So also regard to animals of all classes and of plants If species are in general of hybrid origin Where are the stocks which combine in themselves the habits, properties and organs Of which all the intervening species ought to afford us mere modifications Recapitulation of the arguments from hybrids I shall now conclude this subject by summing up in a few words The result to which I have been led by the consideration of the phenomena of hybrids It appears that the evasion of individuals of the instinct species to the sexual union is common to animals and plants And it is only when the species approach near to each other in their organization and habits That any offspring are produced from their connection Mues are of extremely rare occurrence in a state of nature And known samples are yet known of their having procreated in a wild state But it has been proved that hybrids are not universally sterile Provided parent stocks have a near affinity to each other Although the continuation of the mixed race for several generations Appears it there to have been obtained only by crossing the hybrids with individuals of pure species An experiment which by no means bears out the hypothesis that a true hybrid race could ever be permanently established Hence we may infer that evasion to sexual intercourse is, in general, a good test of the distinctness of original stocks Or of a species And the procreation of hybrids is a proof of the near affinity of species Perhaps, hereafter, the number of generations for which hybrids may be continued Before the race dies out, for it seems usually to generate rapidly May afford the zoologist and botanist an experimental test of the difference in the degree of affinity of allied species I may also remark that if it could have been shown that a single permanent species had ever been produced by hybridity Of which there is no satisfactory proof, it might certainly have lent some countenance to the notions of the ancients Respecting the gradual deterioration of created things But none whatsoever to Lamarck's theory of their progressive perfectibility For observations, have we there to show that there is a tendency in mule animals and plants to degenerate in organization It was before remarked that the theory of progressive development arose partly from an attempt to ingraft the doctrines of the transmutationists Upon one of the most popular generalization in geology But we have seen in the 9th chapter that the modern researches of geologists have broken at many points the chain of evidence One supposed to exist in favor of the doctrine that, at each successive period in the Earth history, animals and plants of a higher grade Or more complex organization have been created The recent origin of man and the absence of all signs of any rational being holding an analogous relation to former states of the animate world Affords one and perhaps in the present state of science the only argument of much weight in support of the hypothesis of a progressive scheme But none whatsoever in favor of the fancy devolution of one species out of another Theory of degradation of intellect as shown by the fashion angle When the celebrated anatomist Kemper first attempted to estimate the degrees of sagacity of different animals and of the races of man By the measurement of the fashion angle, some speculators were bold enough to affirm that certain simie, or apes Deferred as little from the most savage races of man as those do from the human race in general And that a scale might be traced from apes with foreheads with lanus low To the African variety of the human species and from that to the European The fashion angle was measured by drawing a line from the prominent center of the forehead to the most advanced part of the lower jaw bone And observing the angle which it made with the horizontal line And it was affirmed that there was a regular series of such angles from birth to the mamalia The gradation from the dog to the monkey was said to be perfect and from that again to man One of the ape tribe has a fashion angle of 42 degrees And another which approximated the nearest to man in feature an angle of 50 degrees To this succeed, longo sed proximus intervallo The head of the African negro, which as well as that of the Kaumuk, forms an angle of 70 degrees While that of the European contains 80 degrees The Roman painters prefer the angle of 95 degrees And the character of beauty and sublimity so striking in some works of Christian sculpture Has in the head of the Apollo and in the Medusa of Cisocles is given by an angle which amounts to 100 degrees A great number of valuable facts and curious analogies in comparative anatomy Were brought to light during the investigations which were made by Kemper, John Hunter and others To illustrate the scale of the organization And their facts and generalizations must not be confounded with the fanciful systems which white and others deduce from them That there is some connection between an elevated and capacious forehead in certain races of man And the large development of the intellectual faculties seems highly probable And that a long facial angle is frequently accompanied with inferiority of mental powers is certain But the attempt to trace a gradual scale of intelligence through the different species of animals Accompanying the modifications of the form of the skull is a mere visionary speculation It has been found necessary to exaggerate the sagacity of the ape tribe at the expense of the dog And strange contradictions have arisen in the conclusions deduced from the structure of the elephant Some anatomists being disposed to deny the quadrupedity intelligence which he relayed possesses Because they found that the volume of his brain was small in comparison to that of the other mammalia While others were inclined to magnify extravagantly the superiority of his intellect Because the vertical height of his skull is so great when compared to its horizontal length Different races of men are all 01 species It would be relevant to our subject if we were to enter into a further discussion on these topics Because even if a graduated scale of organization and intelligence could have been established It would prove nothing in favor of a tendency in each species to attain a higher state of perfection I may refer the reader to the writings of Blumenbach, Pritchard, Lorenz and more recently Latham For convincing proofs that the variety of form, color and organization of different races of men Are perfectly consistent with the generally received opinion that all the individuals of the species Have originated from a single pair and while they exhibit in men as many diversities Of a physiological nature as appear in any other species We confirm also the opinion of the slight deviation from a common standard of which species are capable The power of existing and multiplying nevrilatitude and in every variety of situation and climate Which has enabled the great human family to extend itself over the habitable globe Is partly says Lorenz the result of physical constitution and partly of the mental prerogative of men If he did not possess the most enduring and flexible corporeal frame His arts would not enable him to be the inhabitant of the old climates And to brave the extremes of heat and cold and the other destructive influences of local situation Yet, notwithstanding the flexibility of bodily frame We find no signs of indefinite departure from a common standard And the intermarriages of individuals of the most remote varieties Are not less fruitful than between those of the same tribe Teedmen on the brain of the fetus invertebrated animals There is yet another department of anatomical discovery to which I must allude Because it has appeared to some persons to afford a distant analogy at least The progressive development by which some of the inferior species may have been gradually Perfected into those of more complex organization Teedmen found and his discoveries have been most fulely confirmed and elucidated by Ser That the brain of the fetus in the highest class of vertebrated animals assumes In succession forms bearing a certain degree of resemblance To those which belong to fishes, reptiles and birds Before it acquires the additions and modifications which are peculiar to the mummiferous tribe So that, in the passage from the embryo to the perfect mummifer There is a typical representation, it is said, of all those transformations Which the primitive species are supposed to have undergone During a long series of generations between the present period And the remotest geological era If you examine the brain of the mammalia At an early stage of uterine life You perceive the cerebral hemispheres consolidated as in fish In two vesicles isolated one from the other At a later period you see them affect the configuration of the cerebral hemispheres of reptiles Still later again they present you with the forms of those of birds Finally they acquire, at the era of birth, and sometimes later The permanent forms which the adult mammalia present The cerebral hemispheres then arrive at the state which we observe in the higher animals Only by a series of successive metamorphoses If we reduce the whole of these evolutions to four periods We shall see that the first are born the cerebral lobes of the fishes And this takes place homogeneously in all classes The second period will give us the organization of reptiles The third, the brain of birds And the fourth, the complex hemispheres of mammalia If we could develop the different parts of the brain in the inferior classes We should make in succession a reptile out of a fish A bird out of a reptile And the mammifera squadruped out of a bird If, on the contrary, we could starve this organ in the mammalia We might reduce it succively to the condition of the brain of the three inferior classes Nature often presents us with this last phenomenon in monsters But never exhibits the first Among the various deformities which organized being may experience They never passed the limits of their own classes to put on the forms of the class above them Never does a fish elevate itself so as to assume the form of the brain of a reptile Nor does the latter even attain deaths of birds Nor the bird death of the mammifera It may happen that a monster may have two heads But the conformation of the brain always remains circumscribed narrowly within the limits of its class Dr. Clark of Cambridge, in a memoir on fatal development, 1845 Has shown that the current labors of Valentin, Rach and Bischoff Disprove the reality of the supposed anatomical analogy between the embryo condition of certain organs in the higher orders And the perfect structure of the same organs in animals of an inferior class The hearts and brains, for example, of birds and mammals Do not pass through forms which are permanent in fishes and reptiles There is only just so much resemblance as may point to a unity of plan Running through the organization of the whole series of vertebrate animals But which lends no support, whatever, to the notion of a gradual transportation of one species into another List of all of the passage in the course of many generations From an animal of a more simple to one of a more complex structure Recapitulation For the reasons therefore detailed in this and the two preceding chapters We may draw the following inferences in regard to the reality of species in nature First, that there is a capability in all species to accommodate themselves to a certain extent To a change of external circumstances, this extent varying greatly according to the species Secondly, when the change of situation which they can endure is great It is usually attended by some modifications of the form, color, size, structure or other particulars But the mutations thus superinducted are governed by constant laws And the capability of sovaring forms part of the permanent specific character Thirdly, some acquired peculiarities of form, structure and instinct are transmissible to the offspring But this consists of such qualities and attributes only as are intimately related to the natural ones and propensities of the species Fourthly, the entire variation from the original type, which any given kind of change can produce May usually be affected in a brief period of time, after which no further deviation can be obtained by continuing to alter the circumstances Though ever so gradually Indefinite divergence, either in the way of improvement or deterioration Being prevented and the least possible excess beyond the defined limits being fatter to the existence of the individual Fifthly, the intermixture of distinct species is guarded against by the aversion of the individuals composing them to sexual union Or by the sterility of the male offspring It does not appear that true hybrid races have ever been perpetuated for several generations, even by the assistance of men For the cases usually cited relate to the crossing of mules with individuals of pure species and not to the intermixture of hybrid with hybrid Sixthly, from the above considerations it appears that species have a real existence in nature and that each was endowed at the time of its creation with the attributes and organization by which it is now distinguished End of Chapter 36 Recording by Emanuela analogy of climate not attended with identity of species botanical geography stations habitations distinct provinces of indigenous plants vegetation of islands marine vegetation in what manner plants become diffused effects of wind, rivers, marine currents agency of animals many seeds pass through the stomachs of animals and birds undigested agency of man in the dispersion of plants both voluntary and involuntary it's analogy to that of the inferior animals Next to determining the question whether species have a real existence The consideration of the laws which regulate their geographical distribution is a subject of primary importance to the geologist It is only by studying these laws with attention, by observing the positions which groups of species occupy at present and inquiring how these may be varied in the course of time by migrations, by changes in physical geography and other causes that we can hope to learn whether the duration of species be limited or in what manner the state of the animate world is affected by the endless vicissitudes of the inanimate Different regions inhabited by distinct species that different regions of the globe are inhabited by entirely distinct animals and plants is a fact which has been familiar to all naturalists since Buffon first pointed out the want of specific identity between the land quadrupeds of America and those of the old world the same phenomenon has in later times been forced in a striking manner upon our attention by the examination of New Holland where the indigenous species of animals and plants were found to be almost without exception distinct from those known in other parts of the world but the extent of this parceling out of the globe amongst different nations as they have been termed of plants and animals the universality of a phenomenon so extraordinary and unexpected may be considered as one of the most interesting facts clearly established by the advance of modern science Scarcely 1400 species of plants appear to have been known and described by the Greeks, Romans and Arabians at present more than 3000 species are enumerated as natives of our own island 841 in other parts of the world there had been now collected 1846 upward of 100,000 species specimens of which are preserved in European herbariums it was not to be supposed therefore that the ancients should have acquired any correct notions of respecting what may be called the geography of plants although the influence of climate on the character of the vegetation could hardly have escaped their observation antecedently to investigation there was no reason for presuming that the vegetable production growing wild in the eastern hemisphere should be unlike those of the western in the same latitude nor that the plants of the Cape of Good Hope should be unlike those of the south of Europe situations where the climate is little dissimilar the contrary supposition would have seemed more probable and we might have anticipated an almost perfect identity in the animals and plants which inhabit corresponding parallels of latitude the discovery therefore that each separate region of the globe both of the land and water is occupied by stink groups of species and that most of the exceptions to this general rule may be referred to disseminating causes now in operation is eminently calculated to excite curiosity and to stimulate us to seek some hypothesis respecting the first introduction of species which may be reconcilable with such phenomena botanical geography a comparison of the plants of different regions of the globe affords results more to be depended upon in the present state of our knowledge than those relating to the animal kingdom because the science of botany is more advanced and probably comprehends a great proportion of the total number of the vegetable productions of the whole earth Humboldt in several eloquent passages of his personal narrative was among the first to promulgate philosophical views on this subject every hemisphere, says this traveler, produces plants of different species and it is not by the diversity of climates that we can attempt to explain why equinoctial Africa has no Lorraine and this new world no heaths why the Calciarii are found only in the southern hemisphere why the birds of the continent of India glow with colors less splendid than the birds of the hot parts of America finally why the tiger is peculiar to Asia and the Erynthorincus to New Holland we can conceive, he adds, that a small number of the families of plants, for instance the Musaceae and the Palms cannot belong to very cold regions on account of their internal structure and the importance of certain organs but we cannot explain why no one of the family of Melastomus vegetates north of the parallel of 30 degrees or why no rosetree belongs to the southern hemisphere analogy of climates is often found in the two continents without identity of productions 843 the luminous essay of Dick and Dole on botanical geography presents us with the fruits of his own researches and those of Humboldt, Brown and other eminent botanists so arranged that the principal phenomena of the distribution of plants are exhibited in connection with the causes to which they are chiefly referable 844 it might not perhaps be difficult to observe as this writer to find two points in the United States and in Europe or in equinoctial America and Africa which present all the same circumstances as, for example, the same temperature, the same height above the sea a similar soil and equal dose of humidity nearly all, perhaps all, the plants in these two similar localities shall be distinct a certain degree of analogy indeed of aspect and even of structure might very possibly be discoverable between the plants of the two localities in question but the species would in general be different circumstances therefore different from those which now determine the stations have had an influence on the habitations of plants stations and habitations of plants as I shall frequently have occasion to speak of the stations and habitations of plants in the technical sense in which the terms are used in the above passage I may remind the geologist that stations indicates the peculiar nature of the locality where each species is accustomed to grow and has reference to climate, soil, humidity, light, elevation above the sea and other analogous circumstances whereas by habitation is meant a general indication of the country where a plant grows wild thus the station of a plant may be a salt marsh a hillside the bed of the sea or a stagnant pool its habitation may be Europe, North America or New Holland between the tropics the study of stations has been styled the topography that of habitations the geography of botany the terms thus defined express each a distinct class of ideas which have been often confounded together and which are equally applicable in zoology in further illustration of the principle above alluded to that differences of longitude independently of any influence of temperature is accompanied by a great and sometimes a complete diversity in the species of plants Dickendall observes that out of 2,891 species of Phenogamous plants described by Perch in the United States there are only 385 which are found in northern or temperate Europe M.M. Humboldt and Bonpland in all their travels through equinoctal America found only 24 species these being all Slyperaceae and Graminae common to America and any part of the old world they collected it is true chiefly on the mountains or the proportion would have been larger for Dr. J. Hooker informs me that many tropical plants of the New World are identical with African species nevertheless the general discordance of these flores is very striking on comparing New Holland with Europe Mr. Brown ascertained that out of 4,100 species discovered in Australia there were only 166 common to Europe and of this small number there were some few which may have been transported there by man almost all of the 166 species were cryptogamic and the rest consist in nearly every case of Phenogamous plants which also inhabit intervening regions but what is still more remarkable in the more widely separated parts of the ancient continent not withstanding the existence of an uninterrupted land communication the diversity in the specific character of the respective vegetations is almost as striking thus there is found one assemblage of species in China another in the countries bordering the Black Sea and the Caspian a third in those surrounding the Mediterranean a fourth in the great platforms of Siberia and Tartary and so forth the distinctness of the groups of indigenous plants in the same parallel of latitude is greatest where continents are disjoined by a wide expanse of ocean in the northern hemisphere near the pole or the extremities of Europe Asia and America unite or approach near to one another considerable number of the same species of plants are found common to the three continents but it has been remarked that these plants which are thus so widely diffused in the Arctic regions are also found in the chain of the Aleutian Islands which stretch almost across from America to Asia and which may probably have served as the channel of communication for the partial blending of the floors of the exotic joining regions it has indeed been observed to be a general rule that plants found at two points very remote from each other occur also in places intermediate Dr. J. Hooker informs me that in high latitudes in the southern ocean in spite of the great extent of the sea floors of widely disconnected islands contain many species in common perhaps icebergs transporting device distances not only stones but soil with the seeds of plants may explain this unusually wide diffusion of insular plants in islands very distant from continents the total number of plants is comparatively small but a large proportion of the species are such as occur nowhere else insofar as the flora of such islands is not peculiar to them it contains in general species common to the nearest main lands 845 the islands of the great southern ocean exemplify these rules the eastern most containing more American and the western more Indian plants 846 Madeira and Tenerife contain many species and even entire genera peculiar to them but they have also plants in common with Portugal Spain the Azores and the northwest coast of Africa 847 in the canaries out of 533 species of Phenogamous plants it is said that 310 are peculiar to these islands and the rest identical with those of the African continent but in the floor of St. Helena which is so far distant even from the shores of Africa that have been found out of 30 native species of Phenogamous class only one or two which are found in any other part of the globe on the other hand of 60 cryptogamic plants collected by Dr. J. Hooker in the same island 12 only were peculiar natural history of the Galapagos Archipelago described by Mr. Darwin affords another very instructive illustration of the laws governing the geographical distribution of plants and animals in islands this group consists of 10 principal islands situated in the Pacific Ocean under the equator about 600 miles westward of the coast of South America as they are all formed of volcanic rocks many of the craters of which there are about 2000 in number having a very fresh aspect we may regard the whole as much more modern in origin than the mass of the adjoining continent yet neither has the flora nor fauna been derived from South America but consists of species for the most part indigenous it's stamped with a character decidedly South American what is still more singular there's a difference between the species inhabiting the different islands of flowering plants for example there are 185 species at present known and 40 cryptogamic making together 225 100 of the former class are new species probably confined to this archipelago and of the rest 10 at least have been introduced by man of 21 species of composite all but one or peculiar and they belong to 12 genera no less than 10 of which genera are confined to the Galapagos Dr. Hooker observes that the type of this floor has an undoubted relation to that of the western side of South America and he detects in it no affinity with that of the numerous islands scattered over other parts of the Pacific so in regard to the birds reptiles land shells and insects this archipelago standing as it does in the Pacific Ocean is zoologically part of America although each small island is not more than 50 or 60 miles apart and most of them are inside of each other formed of precisely the same rocks rising nearly to an equal height and placed under a similar climate they are tenanted each by a different set of beings the tortoises mocking thrushes finches beetles scarcely any two of them ever ranging over the whole and often not even common to any two of the islands the archipelago says Mr. Darwin is a little world within itself or rather a satellite attached to America once it has derived a few stray colonists and has received the general character of its indigenous productions one is astonished he adds at the amount of creative force displayed on so many small barren and rocky islands and still more so at its diverse yet analogous action on points so near each other I have said that the Galapagos archipelago might be called a satellite attached to America but it should rather be called a group of satellites physically similar organically distinct yet intimately related to each other and all related in a marked though much lesser degree to the great American continent 848 number of botanical provinces. Decandole has enumerated twenty great botanical provinces inhabited by indigenous or aboriginal plants and although many of these contain a variety of species which are common to several others and sometimes the place is very remote yet the lines of demarcation are upon the whole astonishingly well-defined 849. Nor is it likely that the bearing of the evidence on which these general views are founded will ever be materially affected since they are already confirmed by the examination of nearly 100,000 species of plants. The entire change of opinion which the contemplation of those phenomena has brought about is worthy of remark. The first travelers were persuaded that they should find in distant regions the plants of some country and they took a pleasure in giving them the same names. It was some time before this illusion was dissipated, but so fully sensible did botanists at last become of the extreme smallness of the number of phenogamous plants common to different continents that the ancient floors fell into disrepute. All grew diffident of the pretended identifications and we now find that every naturalist is inclined to examine each supposed exception with scrupulous severity 850. If they admit the fact they begin to speculate on the mode whereby the seeds may have been transported from one country into the other or inquire on which of two continents the plant was indigenous, assuming that a species like an individual cannot have two birthplaces. Marine vegetation. The marine vegetation is divisible into different systems like those prevailing on the land, but they are much fewer as we might have expected, the temperature of the ocean being more uniform than that of the atmosphere, and consequently the dispersion of species from one zone to another being less frequently checked by the intervention of uncongenial climates, the proportion also of land to sea throughout the globe being small. The migration of marine plants is not so often stopped by barriers of land as is that of the terrestrial species by the ocean. The number of hydrophytes, as they are termed, is very considerable, and their stations are found to be infinitely more varied than could have been anticipated. For while some plants are covered and uncovered daily by the tide, others live at the depth of several hundred feet. Among the known provinces of algae we may mention, first, the North Circumpolar, from latitude 60 degrees north to the Pole. Secondly, the North Atlantic, or the region of Fuchus Proper and Delacerier, extending from latitude 40 degrees north to latitude 60 degrees north. Thirdly, that of the Mediterranean which may be regarded as a sub-region of the fourth or warmer temperate zone of the Atlantic between latitude 23 degrees north and latitude 40 degrees north. Fifthly, the tropical Atlantic in which the Sargassum, Rhodomelia, Corolinia, and Siphonia abound. Sixthly, the South Atlantic where the Fuchus reappears. Seventhly, the Antarctic American, comprehending from Chile to Cape Horn, the Falkland Islands and then surrounding the world south of latitude 50 degrees south. Eighthly, the Australian and New Zealand, which is very peculiar, being characterized among other generic forms by Cysto-Syriae and Fuchsiae. Ninthly, the Indian Ocean and Red Sea, and tenthly, the Chinese and Japanese seas, 851. In addition to the above provinces, there are several others not yet well determined in the Pacific Ocean and elsewhere. There are, however, many species which range through several of these geographical regions of subacquarius vegetation, being common to very remote countries, as, for example, to the coasts of Europe and the United States and others, to Cape Horn and Van Demen's land, the same plants extending also, for the most part, to the New Zealand Sea. Of the species strictly Antarctic, excluding the New Zealand and Tasmanian groups, Dr. Hooker has identified not less than a fifth part of the whole of the British algae, yet is there a much smaller proportion of cosmopolite species among the algae than among the terrestrial cellular plants, such as lichens, mosses, and hepaticae. It must always be borne in mind that the distinctness alluded to between the provinces, whether of subacquarius or terrestrial plants, relates strictly to species and not to forms. In regard to the numerical preponderance of certain forms, and many peculiarities of internal structure, there is usually a marked agreement in the vegetable productions of districts placed in corresponding latitudes, and under similar physical circumstances, however, remote their position. Thus there are innumerable points of analogy between the vegetation of the Brazils, equinoctal Africa, and India, and there are also points of difference where in the plants of these regions are distinguishable from all extra-tropical groups. But there is a very small proportion of the entire number of species common to the three continents. The same may be said if we compare the plants of the United States with that of the middle of Europe. The species are distinct, but the forms are often so analogous as to have been styled geographical representatives. There are very few species of Phenogamous plants, says Dr. J. Hooker, common to Van Diemen's land, New Zealand, and Fewegia, but a great many genera, and some of them are confined to those three distant regions of the southern hemisphere, being in many instances each severally represented by a single species. The same naturalist also observes that the southern temperate as well as the Antarctic regions possesses each of them representatives of some of the genera of the analogous climates of the opposite hemisphere, but very few of the species are identical unless they be such as are equally diffused over other countries, or which inhabit the Andes by the aid of which they have evidently affected their passage southwards. Manor in which plants become diffused. Winds. Plants now consider what means of diffusion independently of the agency of man are possessed by plants, whereby in the course of ages they may be enabled to stray from one of the botanical provinces above mentioned to another, and to establish new colonies at a great distance from their birthplace. The principle of the inanimate agents provided by nature for scattering the seeds of plants over the globe are the movements of the atmosphere and of the ocean, and the constant flow of water from the mountains to the sea. To begin with the winds, a great number of seeds are furnished with downy and feathery appendages, enabling them when ripe to float in the air and to be wafted easily to great distances by the most gentle breeze. Other plants are fitted for dispersion by means of an attached wing, as in the case of the fir tree, so that they are caught up by the wind as they fall from a cone and are carried to a distance. Amongst the comparatively small number of plants known to Linnaeus, 48 genera are enumerated as having winged seeds. As winds often prevail for days, weeks, or even months together in the same direction, these means of transportation may sometimes be without limits, and even the heavier grains may be borne through considerable spaces in a very short time during ordinary tempests. For strong gales which can sweep along grains of sand often move at the rate of about 40 miles an hour, and if the storm be very violent at the rate of 56 miles 852. The hurricanes of tropical regions which root up trees and throw down buildings sweep along at the rate of 90 miles an hour so that forever how short a time they prevail, they may carry even the heavier fruits and seeds over friths of seas of considerable width, and doubtless are often the means of introducing into islands the vegetation of adjoining continents. Whirlwinds are also instrumental in bearing along heavy vegetable substances to considerable distances. Slight ones may frequently be observed in our fields, in summer carrying up haycocks into the air and then letting fall small tufts of hay far and wide over the country, but they are sometimes so powerful as to dry up lakes and ponds and to break off the boughs of trees and carry them up in a whirling column of air. Franklin tells us in one of his letters that he saw in Maryland a whirlwind which began by taking up the dust which lay in the road in the form of a sugarloaf with the winded end downwards and soon after it grew to the height of 40 or 50 feet being 20 or 30 in diameter. It advanced in a direction contrary to the wind and although the rotary motion of the column was surprisingly rapid, its onward progress was sufficiently slow to allow a man to keep pace with it on foot. Franklin followed it on horseback accompanied by his son for three quarters of a mile and saw it enter a wood where it twisted and turned round large trees with surprising force. These were carried up in a spiral line and were seen flying in the air together with boughs and innumerable leaves which from their height appeared reduced to the apparent size of flies. As this cause operates at different intervals of time throughout a great portion of the Earth's surface it may be the means of bearing not only plants but insects, land testaceae and their eggs with many other species of animals to points which they could never otherwise have reached and from which they may then begin to propagate themselves again as from a new center. Distribution of cryptogamous plants It has been found that a great numerical proportion of the exceptions to the limitation of species to certain quarters of the globe occur in the various tribes of cryptogamic plants. Linnaeus observed that as the germs of plants of this class such as mosses, fungi, and lichens consist of an impalpable powder, the particles of which are scarcely visible to the naked eye there is no difficulty to account for their being dispersed throughout the atmosphere and carry to every point of the globe where there is a station fitted for them. Lichens in particular ascend to great elevations, sometimes growing 2,000 feet above the line of perpetual snow at the utmost limits of vegetation and where the mean temperature is nearly at the freezing point. This elevated position must contribute greatly to facilitate the dispersion of those buoyant particles of which their fructification consists. 853 Some have inferred from the springing up of mushrooms wherever particular soils and decomposed organic matter are mixed together that the production of fungi is accidental and not analogous to that of perfect plants. But Fries, whose authority on these questions is entitled to the highest respect, has shown the fallacy of this argument in favor of the old doctrine of equivocal generation. The sporeals of fungi, says this naturalist, are so infinite that in a single individual of reticularia maxima I have counted above 10 millions and so subtle as to be scarcely visible, often resembling thin smoke so light that they may be raised perhaps by evaporation into the atmosphere and dispersed in so many ways by the attraction of the sun, by insects, wind, elasticity, adhesion, etc. that it is difficult to conceive a place from which they may be excluded. 854 The club moss called Lycopodium cernuum affords a striking example of a cryptogamous plant universally distributed over all equinoctal countries. It scarcely ever passes beyond the northern tropic except in one instance where it appears around the hot springs and the Azores, although it is neither an inhabitant of the Canaries nor Madeira. Doubtless its microscopic sporeuels are everywhere present, ready to germinate on any spot where they can enjoy throughout the year the proper quantity of life, moisture, light, and other conditions essential to the species. Almost every lichen brought home from the southern hemisphere by the Antarctic expedition under Sir James Ross amounting to no less than 200 species was ascertained to be also an inhabitant of the northern hemisphere and almost all of them European. End of Chapter 37 Part 1 Chapter 37 Part 2 of Principles of Geology This is a LibriVox recording All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org Principles of Geology by Charles Lial Section 85 Agency of Rivers and Currents In considering in the next place the instrumentality of the aqueous agents of dispersion I cannot do better than cite the words of one of our ablest botanical writers. The mountain stream or torrent, observes Keith, washes down to the valley the seeds which may accidentally fall into it, or which it may happen to sweep from its banks when it suddenly overflows them. The broad and majestic river winding along the extensive plain and traversing the contents of the world conveys to the distance of many hundreds of miles the seeds that may have vegetated at its source. Thus the southern shores of the Baltic are visited by seeds which grew in the interior of Germany and the western shores of the Atlantic by seeds that have been generated in the interior of America. Fruits moreover, indigenous to America and the West Indies such as that of Mimosa scandins, the cashew nut and others, have been known to be drifted across the Atlantic by the Gulf stream on the western coasts of Europe in such a state that they might have vegetated had the climate and soil favorable. Among these the Geolandina bonduck leguminous plant is particularly mentioned as having been raised from a seed found on the west coast of Ireland. Sir Hans Sloane states that several kinds of beans cast ashore on the Orkney Isles and Ireland but none of which appear to have naturalized themselves are derived from trees which grow in the West Indies and many of them in Jamaica. He conjectures that they might have carried by rivers into the sea and then by the Gulf stream to greater distances in the same manner as the seaweed called lenticula marina or Sargasso which grows on the rocks about Jamaica is known to be carried by the winds and current toward the coast of Florida and thence into the North American Ocean where it lies very thick on the surface of the sea. The absence of liquid matter in the composition of seeds renders them very insensible to heat and cold so that they may be carried without detriment through climates where the plants themselves would instantly perish. Such is their power of resisting the effects of heat that Spallanzani mentions to some seeds that germinated after having been boiled in water. Sir John Herschel informs me that he has sewn at the Cape of Good Hope the seeds of the Achesia Lofanta after they had remained for 12 hours in water of 140 degrees Fahrenheit and they germinated far more rapidly than unboiled seeds. He also states that an eminent botanist Baron Ludwig could not get the seeds of a species of cedar to grow at the Cape till they were thoroughly boiled. When therefore a strong gale after blowing violently off the land for a time dies away and the seeds alight upon the surface of the waters or wherever the ocean by eating away the sea cliffs throws down into its waves plants which would never otherwise reach the shores the tides and currents become active instruments in assisting the dissemination of almost all classes of the vegetable kingdom. The pandanus and many other plants have been distributed in this way over the islands of the Pacific. I have before called attention, page 618, to the interesting fact that one-fifth of all the algae found in the Antarctic regions in 1841-3 by Dr. J. Hooker were of species common to the British seas. He has suggested that cold currents which prevail from Cape Horn to the equator and are there meant by other cold water may by their direct influence as well as by their temperature facilitate the passage of Antarctic species to the Arctic Ocean. In like manner the migration of certain marine animals from the southern to the northern hemisphere may have been brought about by the same cause. In a collection of six hundred plants from the neighborhood of the river Zaire in Africa, Mr. Brown found that thirteen species were also met with on the opposite shores of Guiana and Brazil. He remarked that most of these plants were found only on the lower parts of the river Zaire and were chiefly such as produced seeds capable of retaining their vitality a long time in the currents of the ocean. Dr. J. Hooker informs me that after an examination of a great many insular flora he has found that no one of the large natural orders is so rich in species common to other countries as the leguminoseae. The seeds in this order which comprises the largest proportion of widely diffused littoral species are better adapted than those of any other plants for water carriage. The Migration of Plants Aided by Islands Islands moreover and even the smallest rocks play an important part in aiding such migrations for when seeds alight upon them from the atmosphere or are thrown up by the surf they often vegetate and supply the winds and waves with a repetition of new and uninjured crops of fruit and seeds. These may afterwards pursue their course through the atmosphere or along the surface of the sea in the same direction. The number of plants found at any given time on an islet affords us no test whatever of the extent to which it may have cooperated toward this end since a variety of species may first thrive there and then perish followed by other chance comers like themselves. If neither St. Helene nor Ascension have promoted the botanical intercourse between the old and new worlds we may easily account for the fact by remembering that they are not only extremely minute and isolated spots but are also bounded by lofty and precipitous shores without beaches where the seeds of foreign species could readily establish themselves. Currents and winds in the Arctic regions along icebergs covered with an alluvial soil on which herbs and pine saplings are seen growing which may often continue to vegetate on some distant shore where the Ice Island is stranded. Dispersion of marine plants With respect to marine vegetation the seeds, being in their native element may remain immersed in water without injury for indefinite periods so that there is no difficulty in conceiving the diffusion of species wherever uncongenial climates where recurrence and other causes do not interfere. All are familiar with the site of the floating seaweed flung from the rock on oceans foamed to sail where the surge may sweep the tempest's breath prevail. Remarkable accumulations of that species of seaweed generally known as Gulfweed or Sargasso occur on each side of the equator in the Atlantic, Pacific, and Indian oceans. Columbus and other navigators who first entered these banks of algae in the Northern Atlantic compared them to vast inundated meadows and state that they retarded the progress of their vessels. The most extensive bank is a little west of the meridian of Fayal one of the Azores between latitudes 35 degrees and 36 degrees. Violent north winds sometimes prevail in this space and drive the seaweed to low latitudes as far as the 24th or even the 20th degree. Along the northern edge of the Gulfstream Dr. Hooker found Fuchus nodosis and F. Seratus which he traced all the way from latitude 36 degrees north to England. The hollow pod-like receptacle in which the seeds of many algae are lodged and the filaments attached to the seed vessels of others seem intended to give buoyancy and I may observe that these hydrophytes are in general proliferous so that the smallest fragment of a branch can be developed into a perfect plant. The seeds, moreover, of the greater number of species are enveloped with a mucus matter like that which surrounds the eggs of some fish and which not only protects them from injury but serves to attach them to floating bodies or to rocks. Agency of Animals in the Distribution of Plants But we have, as yet, considered part only of the fertile resources of nature for conveying seeds to a distance from their place of growth. The various tribes of animals are busily engaged in furthering an object once they derive such important advantages. Sometimes an express provision is found in the structure of seeds who enable them to adhere firmly by prickles, hooks, and hairs to the coats of animals or feathers of the winged tribe to which they remain attached for weeks or even months and are born along into every region whether birds or quadrupeds may migrate. Linnaeus enumerates 50 genera of plants and the number now known to botanists is much greater which are armed with hooks by which when ripe they adhere to the coats of animals. Most of these vegetables, he remarks, require a soil enriched with dung. Few have failed to mark the locks of wool hanging on the thorn bushes wherever the sheep pass and it is probable that the wool for lion never gives chase to herbivorous animals without being unconsciously subservient to this part of the vegetable economy. A deer has strayed from the herd when browsing on some rich pasture when he is suddenly alarmed by the approach of his foe. He instantly takes to flight, dashing through many a thicket and swimming across many a river and lake. The seeds of the herbs and shrubs which have adhered to his smoking flanks are washed off again by the waters. The thorny spray is torn off and fixes itself in its hairy coat until brushed off again in other thickets and copes. Even on the spot where the victim had many of the seeds which he had swallowed immediately before the chase may be left on the ground uninjured and ready to spring up in a new soil. The passage, indeed, of undigested seeds through the stomachs of animals is one of the most efficient causes of the dissemination of plants, and is, of all others, perhaps, the most likely to be overlooked. Few are ignorant that a portion of the oats eaten by a horse preserve their germinating faculty in the dung. The fact that eating still nutritious is not lost on the sagacious rook. To many, says Linnaeus, it seems extraordinary and something of a prodigy that when a field is well tilled and sown with the best wheat, it frequently produces Darnell or the wild oat, especially if it be manureed with new dung. They do not consider that the fertility of the smaller seeds is not destroyed in the stomachs of animals. Agency of Birds Some birds of the order Poceres devour the seeds of plants in great quantities, which they eject again in very distant places without destroying its faculty of vegetation. Thus a flight of larks will fill the cleanest field with a great quantity of various kinds of plants, as the mellilot treefoil, metacago lupulina, and others whose seeds are so heavy that the wind is not able to scatter them to any distance. In like manner the blackbird and missile thrush when they devour berries in two great quantities are known to consign them to the earth undigested in their excrement. Pulpy fruits serve quadrupeds and birds as food, while their seeds, often hard and indigestible, pass uninjured through the intestines and are deposited far from their original place of growth in a condition peculiarly fit for vegetation. So well are the farmers in some parts of England aware of this fact that when they desire to raise a quick-set hedge in the shortest possible time, they feed turkeys with the haws of the common white thorn, Hortegus oxiathcanta, and then sow the stones which are ejected in their excrement whereby they gain an entire year in the growth of the plant. Birds, when they pluck cherries, slows, and haws, fly away with them to some convenient place and when they have devoured the fruit drop the stone into the ground. Captain Cook, in his account of the volcanic island of Tanna, and of Hebrides, which he visited in his second voyage, makes the following interesting observation. Mr. Forster, in his botanical excursion this day, shot a pigeon in the craw of which was a wild nutmeg. It is easy, therefore, to perceive that birds in their migrations to great distances and even across seas may transport seeds to new aisles and continents. The sudden deaths to which great numbers of forgivorous birds are annually exposed as auxiliary to the transportation of seeds to new habitations. When the sea retires from the shore and leaves fruits and seeds on the beach or in the mud of estuaries it might by the returning tide wash them away again or destroy them by long immersion. But when they are gathered by land birds which frequent the seaside or by waders and waterfowl they are often born inland and if the bird to whose crop they have been consigned is killed they grow up far from the sea. Let such an accident happen but once in a century or a thousand years it will be sufficient to spread many of the plants from one continent to another for in estimating the activity of these causes we must not consider whether they act slowly in relation to the period of our observation but in reference to the duration of species in general. Let us trace the operation of this cause in connection with others. A tempestuous wind blows the seeds of a plant many miles through the air and then delivers them to the ocean. The oceanic current drifts them to a distant continent. By the fall of the tide they become the food of numerous birds and one of these is seized by a hawk or eagle which soaring across hill and dale to a place of retreat leaves after devouring its prey the unpalatable seeds to spring up and flourish in a new soil. The machinery before adverted to is so capable of disseminating seeds over almost unbounded spaces that were we more intimately acquainted with the economy of nature we might probably explain all the instances which occur of the aberration of plants to great distances from their native countries. The real difficulty which must present itself to everyone who contemplates the present geographical distribution of species is the small number of exceptions to the rule of the non-intermixture of different groups of plants. Why have they not supposing them to have been ever so distinct originally become more blended and confounded together in the lapse of ages? Agency of man in the dispersion of plants but in addition to all the agents already enumerated as instrumental in diffusing plants or the globe we have still to consider man one of the most important of all he transports with him into every region the vegetables which he cultivates for his wants and is the involuntary means of spreading a still greater number which are useless to him or even noxious. When the introduction of cultivated plants says de kendole is of recent date there is no difficulty in tracing their origin but when it is of high antiquity we are often ignorant of the true country of the plants on which we feed no one contests the American origin of the maze or the potato nor the origin in the old world of the coffee tree and of wheat but there are certain objects of culture a very ancient date between the tropics such for example as the banana of which the origin cannot be verified armies in modern times have been known to carry in all directions grain and cultivated vegetables from one extremity of Europe to the other and thus have shown us how in more ancient times the conquests of Alexander the distant expeditions of the Romans and Crusades may have transported many plants from one part of the world to the other but besides the plants used in agriculture the numbers which have been naturalized by accident or which man has spread unintentionally is considerable one of our old authors Jocelyn gives a catalog of such plants as had in his time sprung up in the colony since the English planted and kept cattle in New England there were two and twenty in number the common nettle was the first which the settlers noticed and the plantain was called by the Indians Englishman's foot as if it sprung from their footsteps we have introduced everywhere some weeds which grow among our various kinds of wheat and which have been received perhaps originally from Asia along with them thus together with the Barbary wheat the inhabitants of the south of Europe has sown for many ages the plants of Algiers have sown us with the wools and cottons of the east or of Barbary there are often brought into France the grains of exotic plants some of which naturalize themselves of this I will cite a striking example there is at the gate of Montpellier a meadow set apart for drying foreign wool after it has been washed there hardly passes a year without foreign plants being found naturalized in this drying ground I have gathered there a saura a palestina and a paracum crispum this fact is not only illustrative of the aid which man lends inadvertently to the propagation of plants but it also demonstrates the multiplicity of seeds which are born about in the woolly and harry coats of wild animals the same botanist mentions instances of plants naturalized in seaports by the ballast of ships and several examples of which have spread through Europe to the botanical gardens so as to have become more common than many indigenous species it is scarcely a century says Linnaeus since the Canadian Eric Giron or Fleabane was brought from America to the botanical garden at Paris and already the seeds have been carried by the winds so that it is diffused over France, the British islands Italy, Sicily, Holland and Germany as a Swedish naturalist as having been dispersed by similar means the common thorn apple Datura strimonium now grows as a noxious weed throughout all Europe with the exception of Sweden, Lapland and Russia it came from the East Indies and Abyssinia to us and was thus universally spread by certain quacks who used its seeds as an emetic the same plant is now abundant throughout the greater part of the United States along roadsides and about farm yards the yellow monkey flower Memulus luteus a plant from the northwest region of America has now established itself in various parts of England and is spreading rapidly in hot and ill cultivated countries such naturalization takes place more easily thus the Chenopodium Ambrosioides sown by Mr. Burchell on a point of St. Helena multiplied so fast in four years as to become one of the commonest weeds in the island and it has maintained its ground ever since 1845 the most remarkable proof of the extent to which man is unconsciously the instrument of dispersing and naturalizing species is found in the fact that in New Holland America and the Cape of Good Hope the aboriginal European species exceed in number all the others which have come from any distant regions so that in this instance the influence of man has surpassed that of all the other causes which tend to disseminate plants to remote districts of nearly 1600 British flowering plants it is supposed that about 300 species are naturalized but a large proportion of these would perish with a discontinuous of agriculture although we are but slightly acquainted as yet with the extent of our instrumentality in naturalizing species yet the facts ascertained afford no small reason to suspect that the number which we introduce unintentionally exceeds all those transported by design nor is it unnatural to suppose that the functions which the inferior beings extirpated by man once discharged in the economy of nature should devolve upon the human race if we drive many birds of passage from different countries we are probably required to fulfill their office of carrying seeds eggs of fish insects, mollusks, and other creatures to distant regions if we extirpate quadrupeds we must replace them not merely as consumers of the animal and vegetable substances which they devour but as disseminators of plants and of the inferior classes of the animal kingdom I do not mean to insinuate that the very same changes which man brings about would have taken place by means of the agency of other species but merely that he supersedes a certain number of agents and so far as he disperses plants unintentionally or against his will his intervention is strictly analogous to that of the species so extirpated I may observe moreover that if at former periods the animals inhabiting any given district have been partially altered by the extinction of some species and the introduction of others whether by new creations or by immigration a change must have taken place in regard to the particular plants conveyed about with them to foreign countries as for example when one set of migratory birds is substituted for another the countries from and to which seeds are transported are immediately changed vicitudes therefore analogous to those which man has occasioned may have previously attended the springing up of new relations between species and the vegetable and animal worlds it may also be remarked that if man is the most active agent in enlarging so also is he in circumscribing the geographical boundaries of particular plants he promotes the migration of some he retards that of other species so that while in many respects he appears to be exerting his power to blend and confound the various provinces of indigenous species he is in other ways instrumental in obstructing the fusion into one group of the inhabitants of contiguous provinces thus for example when two botanical regions exist in the same great continent such as the European region comprehending the central parts of Europe and those surrounding the Mediterranean and the oriental region as it has been termed embracing the countries adjoining the Black Sea and the Caspian the interposition between these of thousands of square miles of cultivated lands opposes a new and powerful barrier against the mutual interchange of indigenous plants botanists are well aware garden plants naturalize and diffuse themselves with great facility in comparatively unreclaimed countries but spread themselves slowly and with difficulty in districts highly cultivated there are many obvious causes for this difference by drainage and culture the natural variety of stations is diminished and those stray individuals by which the passage of a species from one fit station to another is effected are no sooner detected by the agriculturalist then they are uprooted as weeds the larger shrubs and trees in particular can scarcely ever escape observation when they have attained a certain size and will rarely fail to be cut down if unprofitable the same observations are applicable to the interchange of the insects birds and quadrupeds of two regions situated like those above alluded to no beasts of prey are permitted to make their way across the intervening arable tracts many birds and hundreds of insects which would have found some palatable food amongst the various herbs and trees of the primeval wilderness are unable to subsist on the olive the vine, the wheat and a few trees and grasses favored by man in addition therefore to his direct intervention man in this case operates indirectly to impede the dissemination of plants by intercepting the migration of animals many of which would otherwise have been active from one province to another whether in the vegetable kingdom the influence of man will tend after a considerable lapse of ages to render the geographical range of species in general more extended as Dick and Dole seems to anticipate or whether the compensating agency above alluded to will not counterbalance the exceptions caused by our naturalizations admits at least of some doubt in the attempt to form an estimate on this subject we must be careful not to underrate or almost overlook as some appear to have done the influence of man in checking the diffusion of plants and restricting their distribution to narrower limits End of Chapter 37 Part 2