I 12 



STRUCTURE OF THE SEED 



are called monocotyledons. Further variation will be seen in 

 cone-bearing trees, ferns, etc. 



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. Frequentlv 

 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, re- 

 mains of endosperm. The embryo consists of a stem which is differen- 

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

 above in an epicoty] (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 cotyledons where they subdivide, forming a net- 

 work of veins. B, section of seed of water lily, after Conard — c, 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, D). 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. 



