234 



MORPHOLOG Y. 



is developing it derives its nourisliment from the endosperm (or 

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

 It 



Sn_- 



^ 



>< 



Fig. 3°7- 

 Fertilization of cottoii. 

 pollen tube ; Sn, synergids ; E, 

 egg, with male and female nu- 

 cleus fusing. (Duggar.) 



the integuments increase 

 in extent and harden as 

 the seed is formed. 



461. Perisperm. — In 

 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, (thewater- 

 lily family, the pepper I'lg. 308. 



^ ^ ' 1 -I i. Diagrammatic section or ovary and ovule at time 



family, etc.,) a portion of of fertilization in angiosperm. y, fimlcle of ovule ; 



^' ' / x^ n^ nucellus; ;«, micropyle ; b, antipodal cells of 



the nucellus remains in- embryo sac ; c, endosperm nucleus ; /; egg cell and 



synergids; ai, outer integument of ovule; 2 7, inner 

 tact in the mature seed, integument. The track of the pollen tube is shoYn 



down through tlie style, walls of the ovary to the 

 In such seeds the remain- micropylar end of the embryo sac. 



ing portion of the nucellus is the perisperm. 



462. 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- 



