24 ESSENTIALS OF BOTANY 
is known asthe peg. Study a good many seedlings and try 
to find out what the lengthening of the hypocotyl, between 
the peg and the bases of the cotyledons, does for the little 
plant. Set a lot of squash seeds, hilum down, in moist 
sand or sawdust and see whether the peg is more or less 
developed than in seeds sprouted lying on their sides, and 
whether the cotyledons in the case of the vertically planted 
seeds usually come out of the ground in the same condi- 
tion as do others. ; 
31. Disposition made of the Cotyledons. — The cotyledons 
of the squash during the growth of the seedling increase 
greatly in surface, acquire a green color and a generally 
leaf-like appearance, and, in fact, do the work of ordinary 
leaves. In such a case as this the appropriateness of the 
name seed-leaf is evident enough,— one recognizes at sight 
the fact that the cotyledons are actually the plant’s first 
leaves. In the bean the leaf-like nature of the cotyledons 
is not so clear. They rise out of the ground like the squash 
cotyledons, but then gradually shrivel away, though they 
may first turn green and somewhat leaf-like for a time. 
The development of the plumule seems to depend some- 
what on that of the cotyledons. The squash seed has coty- 
ledons which are not too thick to become useful leaves, 
and so the plant is in no special haste to get ready any 
other leaves. The plumule, therefore, cannot readily be 
found in the unsprouted seed, and is almost microscopic 
in size at the time when the hypocotyl begins to show 
outside of the seed-coats. 
32. Root, Stem, and Leaf. — By the time the seedling is 
well out of the ground it usually possesses the three kinds 
of vegetative organs, or parts essential to growth, of ordinary 
flowering plants, 7.¢., the root, stem, and leaf, or, as they 
