186 BOTANICAL GAZETTE [MARCH 
which is composed of rather large, thin-walled cells without inter- 
cellular spaces, is relatively thick, with an abundance of starch 
deposited in the cells surrounding the central region. In the 
younger stems cells filled with tannin are quite abundant, but in the 
older stages these are less common. This cortical area is traversed 
by the outgoing leaf traces, and numerous roots digest their way 
down through it. The leaf traces are single in the younger stages, 
but in the older levels these bifurcate before entering the stipules. 
Because of the spiral arrangement of the leaves, the leaf traces 
are arranged in zones which exhibit a spiral appearance in cross- 
section, in which the younger are closer to the center than the 
older. No fusing of leaf traces or a branch from one leaf trace 
with that of another takes place. The leaf traces pass outward 
directly. 
The central region consists of the vascular tissue, imbedded 
in a ground tissue which may be called the central parenchyma. 
This parenchyma does not differ markedly from the cortical tissue 
except that the cells are somewhat smaller, have thinner walls, 
and less starch. In the first few stages there is a conspicuous 
endodermis, but in the older stages there is no such layer-of cells 
which marks off the central region from the cortex, and the central 
parenchyma passes insensibly into the former. The central vascular 
tissue consists of a strand which appears more or less crescent- 
shaped in cross-section. The xylem is endarch and is completely 
surrounded by phloem. From one edge of this strand leaf traces 
are given off, and this contribution is always from the same edge 
in the same plant (figs. 3,4). On the outer side of the other edge 
of this central strand a root stele is joined, usually at about the 
same level that the leaf trace is given off. The vascular tissue 
thus contributed to the leaf traces is made good on the other edge 
in two ways, by an increase of vascular tissue on the edge 
itself and by the addition of commissural strands. From the edge 
of each leaf trace abutting on the opening in the central strand a 
commissural strand is given off where the leaf trace is freeing 
itself from the central strand. This bends outward and _ passes 
diagonally upward and fuses with the opposite edge of the central 
strand just below where the next root above is attached (figs. 9-15). 
