257 
Cone and Fertile Stem of Equisetum. 
the axis at the point of insertion of the annulus does not show itself in the 
formation of fresh parenchymatous meshes above this region. I am inclined 
to think that the development of normally sporangiferous annuli is a new 
character in the phylogeny of the genus, though sporangiferous annuli are 
not uncommon as abnormalities in several species. In other words, I believe 
that the sporangia have, in the phylogeny, spread to regions which were not 
at first sporangiferous. If the development of sporangia on the Equise- 
taceous annulus is a fresh character it would necessitate the provision of 
a vascular supply for the nutrition of the spores. The fact that all the 
vascular strands observed in annuli of E ., giganteum ran to points of insertion 
of sporangia, and that the point of insertion of each sporangium was marked 
by the termination of a vascular strand, would seem to show that there is 
a correlation between the development of sporangia and vascular strands by 
the annulus. In fact, if the development of sporangia on the annulus be 
regarded as a character acquired relatively recently in the phylogeny, it- is 
hard to escape from the conclusion that the vascularization of the annulus 
is a change connected with the adoption of this function. There are very 
strong reasons for regarding the annulus as a reduced whorl of leaves. Its 
general appearance and the numerous intermediate forms between leaf- 
sheath and annulus recorded by Milde (Milde, p. 166) and other observers 
support this view. 
We know of another reduced type of leaf-sheath in Equisetum , namely 
the ochreola of Milde. This structure has been shown to be nothing but 
the basal whorl of leaves of a branch. The lowest whorl of leaves of each 
branch appears always to consist of fewer members than the other whorls. 
Its sheath does not show the commissural furrows so characteristic of the 
points of junction of the leaves of other sheaths. Duval-Jouve states (p. 67) 
that the basal sheaths of the branches contain no tracheides, but Milde has 
shown that its largest tooth, situated on the abaxial side of the branch, may 
possess a small vascular bundle (Milde, p. 157, and PI. II, Fig. 36). Here, 
then, the results of the reduction of an undoubted leaf-sheath appear to be, 
besides the reduction in number of its members, the loss of vascular 
elements and the absence of commissural furrows. The general lines on 
which the reduction of the leafy whorl has proceeded in the annulus and 
ochreola are strikingly similar. Loss of vascular traces occurs in both, 
and the absence of commissural furrows in the ochreola may be regarded as 
the first expression of a process which, if carried farther, might well be 
expected to lead to an obliteration of the lines of demarcation between the 
members and to the development of the tissues of the sheath as a homo- 
geneous mass. This is what I believe to have occurred in the annulus. 
Perhaps, however, the most important evidence is that derived from the 
anatomy of the axis near the insertion of the annulus. In my reconstruc- 
tions of the steles of the cones of E. arvense , E. palustre, E. limosum > 
