 On your screen is an enlarged ovary of a flower that has a single ovule and this is an image showing fertilization, the pollen tube bringing in two male gametes, one fuses with the egg to form zygote which is deployed and the other male gamete fuses with the polar nuclei to give rise to the primary endosperm nucleus which is triploid. And we discussed how all this happened in our previous video. Now let's start the story post fertilization. Post fertilization this ovary that you see will gradually turn into a ripe juicy fruit and this ovule will develop into a seed. The zygote will later give rise to a baby plant when the seed is sown and this primary endosperm nucleus will provide nourishment as this zygote grows. Now let's have a look at our flower as a whole. So here is a flower whose ovary has so many ovules inside and post fertilization this ovary will swell up and grow into a fruit and the ovules inside they will form seeds inside the fruit and the seeds if you sow them later it will grow into a plant and that plant will later be your flowers those flowers will be fertilized they will form fruits again and the cycle continues. Amazing right? And also if you are wondering what happens to the other parts of the flower the petals and the male parts well they will eventually dry up and fall off from the plant because their role is done. Post fertilization they have no role to play. Alright now that we know how a fruit is formed from a flower let me ask you about one of my favorite fruits that is the coconut. Now can you tell which part of the ovary gives rise to this refreshing coconut water? And also sometimes we get this white coconut meat or the coconut kernel inside. Now which part do you think gives rise to that? Let's find out and for that we need to go back to the picture of the ovary and this time we have only labeled the zygote and the primary endosperm cell. Now this is the most interesting part of the video as we will see how this ovary slowly converts into a coconut. So the outermost layer that I told converts into a ripe juicy fruit in case of a coconut that doesn't happen. Here it gets converted into an inedible part. Now this is a picture of a coconut which is cut into half longitudinally and like in any fruit the ovary gives rise to primarily three distinct parts. The very outermost part is called the exocarp. The inner husky portion in case of coconut which is of whitish in color is called the mesocarp and the inner stony hardest part is called the endocarp. All these three parts feels and looks very different yet they are formed by the ovary alone. Now let's move inside the ovary. We have an ovule here and ovule is the part that is going to give rise to the inner part of the coconut. Now you might think that hey she just told us that the ovule gives rise to seeds but we don't get any seed inside coconut instead we get water and coconut kernel here. Well let me tell you that the water and the kernel is a part of the seed. Yes, anything inside the endocarp is made of this ovule and is considered a seed and let's see how that happens. And we will begin with the outer covering of the ovule. The outer covering which we call the integuments they form the outer covering of the seed and in case of coconut it forms a very thin brown layer which we call the testa. So this integuments it forms a very thin layer inside the endocarp very thin brown layer which we call the testa. Now testa is a Latin origin word which simply means shell and I think it is called so because it covers or shells the zygote which is very important because it will form the next generation right? It will form the baby plant and testa does the job of protecting it. And just like in coconut every monocod will have this integuments converted into this single layer called testa. But in case of dichots this integuments forms another layer an additional layer inside the testa which they call the tegmin, tegmin it is also a Latin word that simply means covering. Here I have made them quite far apart but actually in seeds they are very closely stuck together and it is considered that in case of monocods both these fuse together just to form a single layer called testa while in case of dichots we see them separately. Now you might wonder that this integuments it do not cover the ovule completely there is an opening called a micropile. What about the seed codes the testa and tegmin do they also have the opening? The answer is yes they have small pores in them for the exchange of water and oxygen because they are vital for seed germination. And even with the pores the testa and tegmin forms a highly protective seed covering or the seed code. And now that we are talking about coconut which is a monocod let's get rid of the tegmin. Well now moving further inside the ovule the next layer that we see is this yellow layer. Well this is a layer of new cellar cell we call it new cellus and one of this cell grew and developed into an embryo sac remember. Now in most fruits this embryo sac while it develops it feeds on this new cellus and completely consumes this new cellar cells and that's exactly what happens in case of coconut. We don't see this new cellar cell here in case of coconut but we do have some very famous examples like coffee and black pepper. In them it is seen that the embryo sac do not completely consume the new cellar cell layer and it persists even in the mature state. So in fruits where the new cellus is found even in the mature state we no longer call them new cellus instead we call them the perisperm. So perisperm comes from a Greek word where peri means around and sperma means seed. So it is a nutritive tissue which is found around the seed or I should say around the embryo sac. And since we don't have this perisperm in case of coconut we immediately get this embryo sac after the testa. Now in the embryo sac we have a zygote and the primary endosperm cell. Now the thing here to be noted is that the zygote can only grow and it can develop if it has something to feed on. Something from which it can derive its nourishment and that requirement is fulfilled by the primary endosperm cell. This cell multiplies to form a nutritive tissue. So until and unless there is a decent amount of endosperm formed inside the ovule we will not see any growth in the zygote. And guess what? This endosperm is the water that we get inside the coconut. Well now you know the answer. This is where you get the coconut water from. But wait what about the coconut kernel? Well even that is formed out of the endosperm. Confused? Well I was confused too but I got to know that it is possible because of the pattern of division this endosperm follows. So if we consider this to be the endosperm cell here the first few divisions will be nuclear division. That I mean that the nuclei will divide repeatedly without the formation of cell walls around them. So there will be a lot of nuclei that will be very loosely packed because there is no cell wall bounding it. And this is what is the coconut water. And at a later stage the nuclei are pushed towards the periphery and that creates a large central vacuole. Now the subsequent divisions of this nuclei that is at the periphery will take place with proper cytoplasmic division. Let's say this nuclei if it divides now again then there will be a proper cell wall formation around it. And multiple layers of the cell with cell wall together forms a hard tissue and that is what is the coconut kernel. And this is why we do not get coconut kernel in tender coconuts. The other day I had coconut water and there was no kernel inside it. But if this was a mature one I would have definitely found a kernel. And this type of cell division of endosperm is called free nuclear division. Now there is another fruit which looks like tiny coconuts. These are called areca nuts or we commonly call it the beetle nut. The endosperm development is quite similar to coconut but the difference is that the embryosac cavity is quite small and this cellular layer of endosperm gradually grows and fills the entire embryosac. So if we cut it open we will see that the entire embryosac is filled with the endosperm cell. And apart from this we also have common examples that we consume every day like maize, wheat, rice, etc. whose endosperm follows this free nuclear pattern of division. Now there can be multiple ways by which this endosperm may divide in different fruits. Let's discuss about two more in this video. So the next one is called cellular endosperm division in which every nuclear division is followed by cytoplasmic division. By that I mean every nuclear division is followed by proper cell wall formation. So 2 cell becomes 4, 4 becomes 8 and we get a proper cellular endosperm right from the beginning. We got cellular endosperm even here but we got it at a later stage right. So in cellular endosperm we get proper cells right from the beginning. And few common examples are mingolia, petunia, etc. And moving on to the third type we call it the halobial type of cell division where we will see a mix of both a free nuclear and cellular division. So initially there will be a proper cell wall formation between two cells but as you can see there will be unequal division of cytoplasm. If we consider this to be the micropile end which means the opening at the ovule here this is called the micropile area and it's opposite is called the cellazolent. So at the micropile area we will see a large cell and at the cellazolent we will see a small cell. Now after a single proper cellular division we will see nuclear divisions happening. So there will be repeated nuclear divisions in this cell, there will be too much activity in the micropile area and very less activity that means very less nuclear division in the cellazol area. And at a later stage there will be proper cell wall formation around each nuclei. And there is a whole order called haloby that follows this type of division of endosperm. And common examples are grape hyacinth, foxtail lilies, etc. Now no matter what type of division the endosperm follows its sole purpose is to provide nourishment to the growing embryo. And do you know how the growing embryo of a coconut looks? Well I was amazed to see that the embryo of coconut was sold as street foods. So this bulging portion that you see it is the growing embryo that is feeding on the endosperm and gradually it will pop out of the seed as a sapling. Until the sapling becomes self-sufficient it thrives on the endosperm. Now just like new cellars it can be completely consumed or it can persist in the mature seed. Just like we get the endosperm in mature coconuts. So depending on the presence or absence of endosperm in mature seeds the seeds are divided into two types albuminous and non-albuminous. Well this comes from the word albumin which is the white part of the egg and endosperm of seeds also have similar appearance milky white. So albuminous seed retain some part of endosperm in the seed and the example can be maize, barley, sunflower or most monocots and non-albuminous seeds refers to those that consume the entire endosperm during the development and the examples are pea, ground nut etc. And just like how our favorite drink inside a coconut is a blessing of the endosperm of the seed you would love to know that our favorite snack popcorn is also possible because of the endosperm inside the corn kernel. When we heat the corn kernel the endosperm inside heats up it produces steam and then bursts out as our favorite popcorns.