Elementary Biology. 



cell wall (compare the period of rest after sexual union in 

 Spirogyra and other types). Meanwhile rapid subdivision 

 of the secondary nucleus of the ovospore (embryo-sac) takes 

 place, accompanied by the aggregation of protoplasm round 

 the new nuclei to form cells. The result is a mass of 

 cellular tissue, the endosperm, whose function it is to pro- 

 vide nourishment for the embryo about to be developed. 

 In relation to the development of the embryo and the 

 formation of a store of nourishment, it may be well to note 



FIG. 89. -Viola tricolor. (Sachs.) 



A, longitudinal section of anatropous ovule after fertilisation. //, pla- 

 centa ; /, swelling on the raphe ; a, outer integument ; /, inner inte- 

 gument ; /, pollen-tube entering micropyle ; e, embryo-sac, with the 

 fertilised ovum at the micropyle end, and numerous endosperm cells at 

 the other. B, apex of embryo-sac, e, with young embryo, eb, of three 

 cells, and one cell forming the suspei.sor. C, same, further advanced. 



the existence in the funicle of a fibro-vascular strand, a 

 feature absent from the funiculi of the lower types, as being 

 unnecessary owing to the simplicity and short life of the 

 sporangium (Selaginella^ or to the fact that the embryo is 

 not developed in the sporangium at all (Pteris). The ovo- 

 spore now increases greatly in size and becomes completely 

 filled with the endosperm, which appears first round the 



