SMITH: DIOSCOREA VILLOSA 553 
THE SEEDLING 
In the mature seed, the embryo is very small in proportion 
to the size of the seed. On germination the cotyledon increases 
rapidly in size (Fic. 28, c), filling the entire fissure which has been 
referred to as formed within the endosperm, and remaining within 
it. The basal part of the cotyledon elongates, forming a trough- 
shaped petiole in whose hollow the first secondary leaf lies. The 
primary root elongates rapidly and soon begins to give off second- 
ary roots. The first secondary leaf elongates, then arches itself 
until its tip becomes free from the seed coats. Beccari (1870a) 
says that in Dioscorea bonariensis the first secondary leaf is bent 
over so that the upper surface of the lamina lies against the 
petiole until the entire leaf emerges. In D. villosa the leaf is not 
bent over while in the seed, but assumes the position described 
by Beccari on freeing itself from the seed and retains it until it is 
well above ground. In the seedling illustrated in Fic. 28, the 
second, third, and fourth secondary leaves have already begun 
to develop. 
The three bundles of the cotyledon fuse in the petiole to form 
a single massive bundle (Fic. 27) which extends the entire length 
of the petiole, is clearly recognizable in the hypocotyl (Fic. 26, ?), 
and forms one of the poles of the tetrarch root (FIG. 25, t). This 
condition differs from that in Tamus, in which, according to Miss 
Sargant (1903), the symmetry of the root stele depends upon 
plumular traces alone. No traces of cambium, such as often 
occur in monocotyledonous seedlings, were found. Each second- 
ary leaf has three bundles. Excepting the traces from the 
second and third secondary leaves, no vascular strands are present 
in the seedling that are not represented in the embryo by pro- 
cambial tissue. 
There are eight bundles in the hypocotyl (Fic. 26). The 
largest one (t) is continuous with the cotyledonary bundle. Of 
the remaining bundles, the three largest (it) are continuous respec- 
tively with the three bundles of the first secondary leaf. The 
hypocotyl is short, as in most monocotyledons, so that the bundles 
of the hypocotyl converge rather rapidly as they enter the root 
and are consequently difficult to follow. It is evident, however, 
that branching of the phloem groups of the four main bundles 
