aS Reictesioe 
1907] HOLM—RUELLIA AND DIANTHERA 323 
and the cells are more roundish in cross-sections; while the inner- 
most, which occupies the greater portion of the internode, is a very 
open tissue with no chlorophyll, but with some small deposits of 
starch. The intercellular spaces are quite wide and the general 
structure of the cortex agrees with that of an aquatic plant. Six 
peripheral steles are located inside the six collenchymatic strands, 
while a seventh occupies the center of the internode. They are all 
orbicular in transverse sections and each has a thin-walled, completely 
closed endodermis, inside of which is another sheath of about two 
layers of thin-walled stereomatic tissue. The mestome bundles of 
the peripheral steles are collateral and arranged in an arch toward 
the periphery of the stem, while the inner face of the steles is occupied 
by a pith and a few scattered strands of pure leptome (fig. 14, L). 
The central stele shows the same structure as the peripheral. Fig. 
13 shows the mestome of one of the peripheral steles; there are a few 
strata of cambium inside the leptome, and some young (three) vessels 
besides older ones in two rays with thin-walled parenchyma between. 
The node above this internode shows at once a change in the disposi- 
tion of the steles, that is, four of the peripheral have fused together 
in pairs so as to form two large steles of triangular outline, while the 
central and the remaining two peripheral are unchanged. The steles 
that thus fuse together in the node are those of the internode which 
are marked S in jig. 9, and between which there is an isolated strand 
of collenchyma. 
In this node the thin-walled collenchyma ‘annie the cortex 
completely, which is here almost destitute of chlorophyll and which 
represents a more compact tissue than in the internode below. No 
raphidines were observed in the node, but many crystals of various 
kinds, needle-shaped, rhombic, prismatic, etc., abound in the pith of 
the broader steles. 
A dilation of some of the steles thus takes place in the node, 
resulting in the gradual concrescence of two steles on each side of the 
node. From the union of these steles each of the two opposite 
leaves receives three mestome cylinders, readily observed in the petiole 
as one central, very broad, and arch-shaped cylinder, with a much 
smaller one on either side. By following the structure of several 
internodes of a single shoot, I noticed that the central stele is not 
