128 



Elementary Botany 



or of the perisperm, or of both, persists, forming the so-called 

 albumen, so that this latter may consist of endosperm, or of 

 ■ perisperm, or of both. 



In the fertilisation of the Fir trees and their allies there is 

 a modification of this process. In the first place the pollen 



A 



Fig. ■itiT .— Viola, tricolor. A, longitudinal section of anatropous ovule after fertilisa- 

 tion : pi, placenta ; w, swelling on the raphe; router, /, inner integument ; >, pollen- 

 tube entering micropyle ; e, embryo-sac, with the fertilised germinal vesicle at the 

 micropyle end, and numerous endosperm cells at the other. _ B, apex of embryo-sac, 

 e, with young embryo, eh^ of three cells, and one cell forming the suspensor or pro- 

 embryo. C, same, further advanced. (After Sachs.) 



grains divide into two cells before pollination, and the tube, 

 instead of being formed from the entire grain, is produced by one 

 of the cells (fig. 249). In the next place the ovules, instead of 



being enclosed in an ovary, 

 are naked (whence the plants 

 are said to be gymnosperms, 

 or naked-seeded plants, whilst 

 other flowering plants are an- 

 giosperms, or enclosed-seeded 

 plants), so that the pollen falls 

 direct upon the micropyle (fig. 

 250). 



Fig. il^Z.— Viola tricolor. Posterior part 

 of embryo-sac : e^ wall ; S^ cavity of 

 the cbU ; K^ K, young endosperm cells 

 formed by free cell formation in the 

 protoplasm, pr. (After Sachs.) 



The embryo-sac soon after pollination is filled with endo- 

 sperm, which disappears after a short while, and a second 

 quantity is subsequently formed. In the upper part of this 



