130 STRUCTURAL BOTANY 



f. Development of the Embryo 



The effects of fertilisation are, that the ovum 

 develops into the embryo, the ovule into the seed, 

 and the pistil into the fruit. We will first con- 

 sider the development of the embryo or young 

 plant, for this is the really important process, 

 to which the changes in the ovule and pistil are 

 subservient. 



The immediate result of fertilisation is that the 

 ovum surrounds itself for the first time with a cell- 

 walL Its nucleus, which, as we have seen, has been 

 formed by the fusion of a generative nucleus from a 

 pollen-grain with the original nucleus of the ovum, 

 next undergoes division. This division of the nucleus 

 is followed by that of the cell, which divides by a 

 transverse wall into two cells. Eepeated transverse 

 divisions then go on, until we have a row of several 

 cells (see Fig. 46, A) attached at one end to the wall of 

 the embryo-sac near the micropyle, while the other end 

 of the row hangs freely in the interior of the sac. The 

 last cell at the free end is nearly spherical, and larger 

 than the rest. The whole structure at this stage is called 

 the pro-embryo. The round cell at the end is called 

 the embryonic cell ; the rest of the row is the suspensor. 

 From the " embryonic cell " the greater part, but not 

 the whole, of the young plant is formed. This cell 

 first divides by three walls, two longitudinal and one 

 transverse (see Fig. 46, A and B, e\ cutting each 

 other at right angles, into eight cells, the octants. 

 Next, each octant divides by a wall parallel to the 



