THE ANATOMY OF A HYBRID EQUISETUM 
229 
around each bundle as in E. limosum. In this respect, E. variegatum var. 
Jesupi is Hke E. variegatum, having a common internal and external 
sheath. Another feature of resemblance to E. variegatum, on the part 
of E. variegatum var. Jesupi, consists in the absence of socalled "nodal 
organs." These parenchymatous swellings, probably akin to lenticels, 
are as Dr. Jeffrey has pointed out (Structure, Development and 
Affinities of the genus Equisetum) present in E. hiemale, and lacking 
in E. variegatum. They seem to be absent also in E. variegatum var. 
Jesupi. Accordingly, as far as rhizome is concerned, E. variegatum 
var. Jesupi is considerably more like E. variegatum than E. hiemale. 
Another fairly constant feature is the nature of the diaphragm, 
which occurs immediately above the node of both aerial and under- 
ground stems. Figure 14 shows a transverse section of E. variegatum, 
and figure 19, a longitudinal one. It is evident from these two photo- 
graphs, that the upper surface of this diaphragm is covered with a layer 
of very thick walled, darkly staining cells. These are the tannin cells. 
They usually occupy the entire pith at this point, and also form large 
masses immediately inside the vascular bundles, extending upward for 
a considerable distance. Beneath them, are thinner walled, paren- 
chymatous elements, which, toward the centre, show a tendency to 
become arranged in longitudinal rows. In E. variegatum var. Jesupi, 
the conditions are different, in that the tannin cells are considerably 
less in extent. Instead of occupying the entire pith, they appear in 
only a part of it (fig. 16). They are not equally developed in every 
node, so that, especially in the aerial stem, a longitudinal section may 
miss them altogether (fig. 21). On the other hand, the cells beneath 
are in distinct, longitudinal rows, forming a true periderm. As in 
other respects, E. hiemale goes one step beyond E.. variegatum var. 
Jesupi. The tannin cells (fig. 18) occur only in isolated masses, and 
often, even in the rhizome, they fail to appear at all (fig. 23). The 
periderm, however, is very well marked, two or three layers of cells 
being lignified. Thus in the development of tannin cells and of nodal 
periderm, E. variegatum- var. Jesupi is intermediate between E. vari- 
egatum and E. hiemale. 
Finally, the cones of these three Equiseta were examined. Figure 
20 represents a section of E. variegatum. In the centre is the sporo- 
phore, above and below which are the sporangia. The uniform size 
of the spores and their elaters coiled around them, are easily distin- 
guished. The character of the wall may be best seen in the case of 
