FERTILISATION AND ITS EFFECTS 277 



certain plants it becomes stored with food and is present in the 

 ripe seed : such stored nucellar tissue is termed perisperm («, 2, 

 Fig. 1 01). 



The fertilisation act brings about the production of an embryo, 

 and stimulates the growth of other parts of the ovule, so that 



771 



Fig. ioi.' — Diagrammatic longitudinal sections of an ovule (i) and the seeds (2, 3, and 4) 

 which may be derived from it. 



jc The ovum which after fertilisation becomes the embryo of the seed ; in micropyle ; 

 ch chalaza ; f funicle ; / coats of ovule ; e embryo-sac ; « nucellus : r radicle of embryo ; 

 c cotyledons of embryo. 



2 and 3 are 'albuminous' seeds, tissues derived from the nucellus and embryo-sac being 

 present m them. In 2 the tissue « is termed perisperm ; it is absent from 3. In 3 the 

 endosperm tissue e produced within the embryo-sac is alone present with the embryo. 



4 is an ' exalbuminous ' seed , both perisperm and endosperm being absent. 



the latter is finally converted into a seed: the corresponding 

 parts of the ovule and the seed are indicated below : — 

 • The Ovale. The Seed. 



The egg-cell or ovum becomes the embryo. 

 ,, integuments ,, „ seed-coats or testa. 



,, micropyle „ ,, micropyle. 



,, funicle „ ,, funicle. 



In so-called ' albuminous ' seeds, the ' albumen ' may re- 

 present storage-tissue developed in the embryo-sac and termed 

 endosperm, or it may be derived from the nucellus, in which 



