NATURE OF PLANTS 



119 



It must be borne in mind that the formation of the seed is 

 also attended with profound changes in the structure of the 

 ovule, and often in the pistil and surrounding parts. Frequently 

 the endosperm grows so extensively as to absorb and replace the 

 cells of the nucellus and thus comes to occupy all the space within 



B 



Fig. 82. Structure of the seed: A, section of an ovule of peppergrass in 

 which the growth of the embryo is nearly complete — ■/, stalk or funiculus 

 attaching ovule to wall of ovary; mi, micropyle; i, integument; en, remains 

 of endosperm. The embryo consists of a stem which is differentiated 

 into a hypocotyl, hy, that ends below in a root, r, and root cap, and above in 

 the plumule, pi, and two cotyledons, c, which curve over and lie one upon the 

 other. V, vascular bundles which extend up through the stem into the coty- 

 ledons where they subdivide, forming a network of veins. B, section of seed 

 of water lily, after Conard — e, embryo surrounded by a layer of endosperm 

 cells; mg, cells of the nucellus; i, integument. 



the coats of the integument, as in the castor bean, morning glory, 

 onion, etc. (Fig. 85, B). The embryo may remain comparatively 

 small as in the cases just cited or it may in turn absorb and 

 replace all the cells of the endosperm and so come to occupy 

 the space within the integument, as in the bean, pea, etc. (Figs. 

 82, A; 83, D). Various other arrangements may result; as for 

 example, there may be remains of the nucellus and endosperm 



