GAMETOPHYTE AND SPOROPHYTE. 



331 



is developing it derives its nourishment from the endosperm (or 

 in some cases perhaps from the nucellus). At the same time 



Sn- 



Fig- 305- 



Fertilization of cotton. pt, 

 pollen tube; Sn, synergids; , 

 egg, with male and female nu- 

 cleus fusing. (Duggar.) 



the integuments increase 

 in extent and harden as 

 the seed is formed. 



661. Perisperm. In 

 most plants the nucellus is 

 ail consumed in the devel- 

 opment of the endosperm, 

 so that only minute frag- 

 ments of disorganized cell 

 walls remain next the in- 

 ner integument. In some 

 plants, however, (the water- 

 lily family, the pepper 

 family, etc.,) a portion of 



the nucellus remains in- embryo sac j \ e, endosperm nucleus ; * egg cell and 



synergids ; #z, outer integument of ovule ; zz, inner 



tact in the mature Seed, integument .The track of the pollen tube is shown 



down through the style, walls of the ovary to the 

 .. In Such Seeds the remain- rnicropylar end of the embryo sac. 



ing portion of the nucellus is the perisperm. 



662. Presence or absence of endosperm in the seed. In 



many of the angiosperms all of the endosperm is consumed by 

 the embryo during its growth in the formation of the seed. This 

 is the case in the rose family, crucifers, composites, willows, oaks, 

 legumes, etc., as in the acorn, the bean, pea and others. In 

 some, as in the bean, a large part of the nutrient substance pass- 



