THE ANATOMY OF A HYBRID EQUISETUM 
227 
continuous between the bundles; all have the sunken stomata char- 
acteristic of the subgenus Hippochaete; all have the stomata in two 
lines down the furrows, rather than scattered as in E. littorale and 
E. limosum; and all have the three sets of canals — central, vallecular 
and carinal. These sections corroborate the statements made above 
in regard to the outline of the stem. In E. variegatum (fig. 7) the 
ridges are sharply biangulate with a carinal furrow. Often in E. vari- 
egatum var. Jesupi (fig. 9) they are rounded, though not infrequently, 
bluntly angled. In E. hiemale (fig. 11) on the other hand, they are 
always rounded. These three photographs show also the relative 
size of the canals. The central an^ vallecular canals of E. variegatum 
have approximately the same diameter; in E. variegatum var. Jesupi, 
the central is considerably larger; and in E. hiemale this is still more 
the case. 
Next to the distribution of the endodermis, the character of the 
bast fibers, with its consequent effect on the distribution of the green 
parenchyma, has been considered by anatomists as the most important 
diagnostic feature. In E. variegatum, there is a considerable mass of 
these fibres under both ridges and furrows, but it is usually heavier 
in the latter position. It extends inward to the border of the vallecular 
canal, thus cutting the green parenchyma at that point. This in- 
terruption of the palisade tissue under the furrows and its continuity 
under the ridges, seems to be invariable in E. variegatum, though Milde 
figures it as continuous around the whole stem. In E. variegatum 
var. Jesupi on the other hand, there is no such constancy. The 
carinal bast is usually more extensive than the vallecular, but, even 
so, the palisade tissue is not uncommonly continuous under it. Figure 
8 shows a section where such is the case. The masses of vallecular 
bast are relatively small, but usually they reach the jacket of cells 
which surround the canals. This variability results in the green paren- 
chyma being sometimes interrupted at only the furrows, sometimes 
at only the ridges, sometimes under both ridges and furrows (fig. 10), 
and rarely being continuous around the entire stem. Not infre- 
quently, due to some irregularity, the carinal bast is pushed to one 
side of the ridge, and a similar displacement may occur to the vallecular. 
Toward the upper left of figure 9 instances of both these may be seen. 
Such a condition is at variance with Eaton's description. He saw 
the interruption of the green parenchyma by the carinal bast, but 
failed to see that by the vallecular. Inasmuch as the writer has had 
