54 Sargant .— Theory of the Origin of Monocotyledons 
plumular stele are much more numerous and better differen- 
tiated in the Ranunculaceous seedlings examined than in 
seedlings of Anemarrhena which have reached the same stage 
of development. In Anemarrhena the plumule lags far behind 
the cotyledon. Moreover, among Dicotyledons a cambium is 
very well developed in the traces of both. Its position is 
indicated by the waved line in Diagram IX. 
The stele of the hypocotyl is elliptical in Delphinium and 
Nigella. The two groups of cotyledonary xylem are placed 
at the extremities of the major axis, while two of the four 
phloem masses fuse with each cluster of plumular phloem 
ABC 
groups (B, Diagram IX). The root-stele becomes diarch at 
once. A considerable part of the metaxylem, as well as 
much of both phloem groups, is derived from plumular 
traces. 
These changes take place in the upper part of the elongated 
hypocotyl, and are commonly complete a few millimetres 
below the first node. 
Several species of Delphinium have the petioles of their 
cotyledons united into a. tube, and I have made a complete 
examination of one such species, probably D. nudicaide. The 
first leaves of this species are developed in the summer after 
germination, and they soon burst out of the sheath formed 
by the base of the united cotyledons (Lubbock, 30, vol. i. 
P- 97)- 
The cylinder formed by the united cotyledons is solid 
