1922] BROWNE—EQUISETUM 457 
bundle. When the xylem of the trace detaches itself from the 
axial wood, it forms an isosceles triangle, sometimes containing 
one or two parenchymatous cells. At the inwardly directed apex 
of the triangle lies the protoxylem. In most cases at least, a 
few of the tracheids at the sides of the wide, outwardly directed 
base of the triangle are derived from the peripheral nodal xylem 
of the bundle. By the time the trace has become free and provided 
with a separate endodermis, its xylem has become or is becoming 
slightly mesarch. As the trace moves out, a bar of metaxylem, 
usually only one cell in depth, forms across the inner end of the 
parenchymatous sheath (fig. 6, stage 3). These tracheids very 
soon die out in passing upward. Although few in number, they 
seem to represent the much greater extent of median supranodal 
xylem of stages 8a and 86 of fig. 2. 
It should be pointed out that, as in the node of the larger 
axis, some elements of the protoxylem, although here only a very 
few, persist on either side of those that depart to the trace. Each of 
the reconstituted bundles possesses two groups, derived respectively 
from the two bundles alternating with it in the internode below. 
Owing to the smaller size of the bundles, these two groups of proto- 
xylem are nearer to one another than in the bundles of the main 
axis. They soon unite, forming with additional elements the proto- 
xylem strands of the new internode. These groups of protoxylem 
traversing the node are very small and inconspicuous, and might 
easily be overlooked or taken for the narrow ends of nodal tracheids. 
It is possible that sometimes one of them may die out and not be 
continued in the internode above, but this could not be satis- 
factorily determined from the material. 
IV. Branches initiated on main stem 
One point in connection with the numerous branches initiated 
on the large young axis of E. gigantewm deserves mention. None 
of these branches, the cells of which were active in process of 
division, had yet broken through the tissues of the leaf sheath of 
the parent axis. As they alternate with the teeth of this sheath, 
their median line coincides with the commissural furrow, or line of 
congenital fusion of two leaves. This furrow projects markedly 
