GAMETOPHYTE AND SPOROPHYTE. 



33' 



is developing it derives its nourishment from the endosperm (or 

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



Sn- 



male and female nu- 

 u's fusing. (Duggar.) 



the integuments increase 

 in extent and harden as 

 the seed is formed. 



661. Perisperm. In tt 

 most plants the nucellus is ' 

 all 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- 

 tact in the mature seed. 

 In such seeds the remain- 

 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- 



Fig. 396. 



Diagrammatic section of ovary and ovule at time 

 of fertilization in angiosperm. f, funicle of ovule ; 

 , nucellus ; m, tnicropyle ; b, antipodal cells of 

 embryo sac ; e, endosperm nucleus ; k, egg cell and 

 synergids ; at, outer integument of ovule ; ii, inner 

 integument. The track of the pollen tube is shown 

 down through the style, walls of the ovary to the 

 micropylar end of the embryo sac. 



