1906] CHRYSLER—NODES OF GRASSES Ti 
be associated with the large number of leaf-trace bundles of the 
monocotyledons, their phylogenetic significance is considerable. 
The ferns and dicotyledons have a comparatively small number of 
leaf-trace bundles; amphivasal bundles are absent in the former 
and rare in the latter group, but are widely distributed in the mono- 
cotyledons, which accordingly appear to represent a more recent 
and highly specialized group. In the most highly organized members 
of the Gramineae, such as Zea, is shown a tendency to reduce the 
number of amphivasal strands, but even in such cases they may 
linger on in the reproductive axis. JEFFREY (9) has called attention to 
the fact that in highly organized families, such as Tridaceae and 
Orchidaceae, these bundles disappear even from the reproductive axis. 
CAMBIUM. 
A feature of the vascular bundles of Avena barbata, not so far 
mentioned, is represented, in fig. 9, which shows a bundle from the 
stem at a distance of about 1™™ above one of the upper nodes. That 
the tissues are immature is shown by the presence of protoplasm 
and a nucleus in certain of the vessels. The shrunken protophloem 
is represented by the dark band at the outer edge of the bundle, and 
the metaphloem as usual has its elements arranged irregularly. 
Between these elements and the vessels are a number of rows of 
flattened cells, radially arranged, corresponding well to the cambium 
of dicotyledons. This feature is not confined to the young stem, 
as is seen in jig. 10, which represents a bundle from above one of 
the lower nodes of the same plant. A few tangential divisions are 
to be seen in the leaf-trace bundle shown in fig. 1, though cambial 
activity here is slight. Toward the node and farther up in the 
internode and sheath, this peculiarity is not shown by the bundles, 
but at the regions mentioned most of the bundles have a more or 
less clear indication of cambium. 
In the leaf-sheath of Andropogon argenteum (fig. 11), at a distance 
of 1-2™™ above its insertion on the stem the larger bundles show 
an unmistakable cambial layer. From the small amount of phloem 
or xylem showing radial arrangement of its elements, it appears 
that the cambium is functional for only a short time. Sections. 
through the leaf-sheath, cut 5™™ above the one shown in the figure, 
still exhibit a layer of radially arranged cells exterior to the xylem, 
