220 THE SEED AND THE SEEDLING 
contains a young plant well started. (2) It can resume 
growth soon after being formed, or it can remain dormant 
for years. This might prevent total loss of seed. (3) It is 
surrounded by a hard testa which prevents the embryo from 
drying out during a long resting period. This enables it to 
remain viable (Latin, vita, life) for many years. (4) It can 
absorb water slowly through the micropyle when covered 
with moist earth. This softens the testa and causes the 
cotyledons to swell, help¬ 
ing to release the embryo. 
(5) The cotyledons con¬ 
tain food for the young 
plant till it can make its 
own. This insures fapid 
growth in the early 
stages, an advantage in 
competition with other 
seedlings. 
198. Growth of the 
Bean Embryo. — When 
the embryo resumes 
growth after a resting 
period, the root breaks 
out of the testa first. 
This is an adaptation, 
for it at once begins to 
absorb water needed for further growth and soon becomes 
firmly imbedded in the soil. The second adaptation is the 
curving of the hypocotyl (hy-po-kot'd: Greek, hypo, 
beneath; kotyle, cavity). This forms a loop on top of 
which is a hard portion, the peg. The hypocotyl grows 
rapidly, causing the arch of the loop to turn from side to 
side, pushing the particles of soil apart and working its way 
to the surface. Then the cotyledons are pulled up as the 
arch straightens. Finally, further growth of the hypocotyl 
Figure 208. — Seeds of Bean and Pea. 
Upper, split, showing embryo. (Only 
the part showing the embryo was saved.) 
Lower, whole, showing markings. A, em¬ 
bryo ; B, plumule; C, root; D, hilum; 
E, micropyle; F, embryo; G, hilum; 
H, micropyle. 
