founded on the Structure of their Seedlings . 33 
are inserted the protoxylem elements. They are not yet 
external. In the diarch root (PI. V, Fig. 12) one proto- 
xylem group is derived from the double cotyledonary trace 
and the other from the plumular traces. The two phloem 
groups are of mixed origin. 
The transition in Zygadenus elegans resembles that of 
Allium precisely, except for the more intimate union of the 
two bundles in the cotyledon. 
Veratrum nigrum. The cotyledon contains a single massive 
bundle throughout its length, but in the sheath two or more 
slender lateral bundles appear. These are ultimately inserted 
on the plumular traces. 
During the transition two crescents of xylem appear, each 
with a protoxylem group at either horn. One crescent is 
derived from the xylem of the cotyledonary double trace : 
the other from the xylem of the lateral and plumular traces. 
The four protoxylem groups are separated by four phloem 
groups : two of these are derived from the double trace and 
the other two from lateral and plumular traces. 
In the absence of sections from allied species the homology of 
this transition must remain uncertain. It would be very readily 
derived from such a form as S cilia sibirica (Diagram III). 
Tricyrtis hirta. The vascular symmetry of this seedling 
presents many interesting features, but it cannot be described 
in detail here. The mature plant is a herbaceous perennial 
with a short creeping rhizome. The hypocotyl of the seed- 
ling is unthickened and of some length. 
The cotyledon is leaf-like, and contains but one bundle. 
This opens out into a very well-marked double bundle a little 
above the first node. Two plumular traces are inserted on the 
double trace at the first node (A, Diagram VIII). When the 
insertion is complete no sign of transition to root-structure is 
observed : the double trace — now surrounded by an endo- 
dermis — is continued downwards in the elongated hypocotyl 
(B, Diagram VIII). Cauline roots are given off from it. 
D 
