1906] CHRYSLER—NODES OF GRASSES 9 
acter shared by all the bundles of such plants. Quite commonly, 
the bundles are surrounded by a layer of parenchyma rich in chloro- 
phyll. This suggests that the node is an active assimilating organ. 
Bundles of the second class—amphivasal bundles as usually under- 
stood—are found in the nodes of the great majority of the grasses 
examined, but are especially numerous in the following species: 
Coix lachryma, Paspalum stolonijerum, Panicum sanguinale, Sor- 
ghum halepense, Leersia oryzoides, Phalaris arundinacea, Calama- 
grostis canadensis, Avena barbata, Panicularia americana, Panicularia 
nervata, Festuca arundinacea, Triticum sativum. The fact that they 
are practically confined to the nodal regions, suggests that they are 
associated with bundle fusions, and this assumption has been amply 
borne out by observation. Further, since the bundles which fuse 
are usually traces of leaves which come off higher up, it appears 
that the occurrence of such bundles is to be referred to the leaves. 
The closed mode of venation, prevalent in the monocotyledons, 
involves that a large number of bundles shall run down parallel to 
one another through the petiole or sheathing base of the leaf. In the 
grasses the numerous bundles are accommodated in the leaf-sheath, 
which frequently encircles the stem for somewhat more than 
360°. The large number of bundles cannot at once find room in 
the vascular ring, which we may believe constitutes the primitive 
stele in both dicotyledons and monocotyledons, according to the 
results of JEFFREY (8), and CHRYSLER (10). Hence the leaf-trace 
bundles, or some of them, pass into the inside of the central cylinder, 
and sooner or later join other bundles. It will be readily seen that 
a bundle lying in the pith has a better chance to orient itself with 
regard to some other bundle which it may join, than has a bundle 
which merely fits itself into a gap in a vascular ring (e. g., the leaf- 
trace of a fern such as Adiantum). Hence it is not surprising to 
find that before two bundles of a monocotyledon fuse, they swing 
around, so that phloem fuses with phloem, and the xylem accordingly 
surrounds the compound bundle. How far beyond the point of 
fusion of the bundles this amphivasal condition persists, is a feature 
which varies greatly. In most of the grasses the collateral structure 
is soon resumed, but the example of Zizania shows that, at the base 
of the stem where the nodes are crowded, the amphivasal condition 
