116 
W. C. Etheridge 
the types are not uncommon, for all of them have been recognizee! among 
the varieties of the present classification. But the establishment of 
groups of varieties according to such fine subdivisions in the form of 
panicles was found to be exceedingly difficult and impracticable. There 
is a clear and constant distinction between the unilateral and equilateral 
forms, but subdivisions of either form, while well defined between certain 
varieties, are transitional between others. In fact, often the panicles of 
the same plant were found to exhibit a transition between certain forms 
described by Nilsson and by Bohmer. It would not be possible, there- 
fore, to establish accurately the group relationship of a large number 
of varieties in a system based on fine distinctions between forms of the 
panicles. There would be uncertainty in many cases as to which of two 
transitional groups should include a given variety. 
In the present classification the A. sativa orientalis group is distinguished 
by its unilateral panicles, and there is no probability of confusing the one- 
sided, appressed panicles of this group with the equilateral, spreading 
panicles of other groups. Beyond this primary distinction, however, 
the form of panicles is employed in but few cases, and then only as a 
supplementary character for the separation of smaller groups. 
The rhachis 
The rhachis, which is that part of the stem running through the panicle, 
commonly shows among the forms of Avena no taxonomic differences. 
It is usually slightly flexuous, and uniform throughout its length. In 
marked contrast to this general form, however, there are a few varieties, 
mostly of the A. sativa orientalis group, in which the rhachis exhibits 
two peculiarities of structure — an extremely flexuous form, and an 
abnormal node at the point from which arises the lowest whorl of branches 
(fig. 15, a). The peculiar node is very striking. It is situated at a 
somewhat geniculate bend in the rhachis, and its diaphragm is usually 
wanting. Lacking a nodal diaphragm, the stem is hollow at this point 
in contrast to its solidity at normal nodes (fig. 15, b). Below the genicu- 
late bend is a normal, although branchless and leafless, node, and the 
two nodes, although in some cases fused, are usually from one to four 
inches apart. The branches probably originate at the outlying normal 
