APPENDIX. 



477 



nuclei, which enter the necks of the archegonia and fuse with 

 the egg cell. 



The fertilised egg grows and divides in such a manner as 

 to form four rows of cells at the lower end of the " primary 

 endosperm." Then these rows separate from each other, and 

 each grows to form an embryo (Fig. 17). Since there are 

 often four or five archegonia, and each fertilised egg gives 



PROTHALLUS CELLS 



A /' ANTHERID. % 



CELL ^m&^ .STALK CELL 



16. Stages in the Germination of the Pollen-Grain. 



A, B, early stages in Picea, the Spruce, where the antheridial cell divides shortly after 

 pollination ; C, late stage in Pinus. 



rise to four young embryos, a single ovule may contain about 

 a score of embryos, which are pushed down into the " primary 

 endosperm " by elongation of their suspensors. Eventually, 

 however, only one of these competing embryos survives in the 

 ripe seed. 



In the meantime the tissue we have called "primary 

 endosperm " grows actively and forms the endosperm of the 

 ripe seed, and the successful embryo which lies in its midst 

 consists of root, shoot, and a circle of about a dozen coty- 

 ledons. The ripe seed is therefore endospermic. It is fur- 

 nished with a thin wing, which is formed from the surface 



