_ 
1904] CHRYSLER—CENTRAL CYLINDER 171 
here also is an internal as well as an external phloeoterma. Certain 
of the strands are amphivasal, and three of these have left the stelar 
ring and run immediately adjacent to it in the medulla. The vascular 
system of this plant evidently represents a condition slightly more 
complicated than that present in_C. borealis. Unfortunately seed- 
lings of neither species of Clintonia have been available, so that the 
origin of the interesting condition seen in the mature stem remains 
unknown. . 
MAIANTHEMUM BIFOLIUM.—The general habit of the plant is 
similar to that described for Clintonia, though the two foliage leaves 
arise from a higher region of the aerial shoot. Fig. 16 represents a 
section through the rhizome a short distance above where it turns 
upward. The heavily cutinized external phloeoterma is a prominent 
feature, and inside of it is a circle of collateral bundles; three amphi- 
vasal bundles run in the medulla, but these do not become leaf traces; 
on the contrary they end as they begin, namely, by joining bundles 
of the vascular.ring. Throughout the horizontal course of the rhi-. 
zome no medullary bundles are present. Several leaf traces are to be 
seen at various stages in their escape from the stele; it will be noticed 
that they cause no break in the continuity of the phloeoterma. 
In the seedling the stele contains pith even in the hypocotyl; as 
the single cotyledonary trace leaves the stele, the phloeoterma bends 
inward around the edges of the gap, but does not lose its continuity; 
the pericycle is continuous with the pith through the gap and no amphi- 
vasal strands are present. To the second leaf three traces are given 
off; the median trace causes the phloeoterma to bend inward, as does 
the cotyledonary trace (fig. 17); the lateral traces emerge exactly as 
in the adult stem (fig. 16). The third leaf receives three traces which . 
leave the stele as do those of the second leaf ; the same is true of the 
fourth and fifth leaves. Comparing the stele of this plant with that 
of Clintonia borealis, the absence of internal phloeoterma and the 
Presence of amphivasal medullary strands in the former are to be 
noted, though these do not make their appearance until a late stage 
of development. 
2MILACINA STELLATA.—As the primary root merges into the hypo- 
cotyl, the stele becomes hollow and the vascular tissue aggregates in 
Several collateral strands at the periphery of the stele. An external 
