NEW FEATURES IN CALAMITES AND EQUISETACEÆ, 287 
and barren periods, as noticed in recent Equiseta and Calamites. Thus the 
largest internodes appear, in a compound species (by which we mean com- 
bining fertile and barren periods), to aggregate towards the centre normally. 
A short internode divides them, preceding a branch-bearing period. 
This feature is noticed in the subgenus Calamitina and in a modified form, 
as remarked, in the other subgenera Stylocalamites and Æucalamites. Та 
combination with the many other features possessed by Calamarieæ and Equi- 
setaceæ in common, this additional character is another argument in favour 
of their union under the group Equisetales. 
Apparently the uniformity in the gradual increase in length of internode 
bears some relation to height. In cases where there are more than the usual 
number in Æquiseta the supernumerary ones, though high up in the stem, are 
sometimes shorter than others below, due to necessity for increased strength 
or dearth of water-supply. 
In some species, e. g. F. sylvaticum, the abnormal decrease is due to the 
overlapping of two or more leaf-sheaths, and the internodes are reduced iu 
length, as before a cone or branch-bearing period, 
In some cases the internodes between branch-bearing nodes after normal 
decrease suddenly elongate. This is doubtless due to habitat, Ё. sylvaticum 
favouring a shady locality. They decrease after a branch-bearing node, as in 
7. arvense, I. maximum, F. pratense. In these the last internode before a cone 
is shortened. It is, then, a fair inference that a foreshortening in length of 
an internode immediately precedes a new cycle of organs, or a grand. period, 
as Strasburger calls it. Occurring at the base of the branchless period, or 
just before the branched whorls, or a cone, as it does in recent /quiseta, it 
presents a strong analogy to the short internode in € 'alamites Schützei, Stur, in 
position and function, and there is good reason to regard them as homologous. 
In the extinct species the branched and branchless whorls occur in combina- 
tion, and not separately as in Zquisetum. Owing to their fragmentary state 
of preservation, a long sequence of internodes has not been examined, and we 
do not know as yet with what stems to correlate the cones, ete. The 
instances adduced on either side, i. e. fossil and recent forms, serve to indicate 
the homology of the strueture. Whether there has been reduction or no, 
we cannot definitely say, but it seems extremely probable, since Equisetum is 
certainly a reduced from. The short internode with the funetion and 
position indicated may thus be regarded as typical of Equisetales in general. 
The details of its variation may be worked out later. The significance it 
affords is that it marks the introduction of an additional organ or series of 
organs and the commencement or conelusion of a period. 
Reeapitulating, it is found that in living plants of Equisetum the shortest 
internode or leaf-sheath separates the root-bearing subterranean portion 
from the aerial branchless stem, and after a gradual increase in length a 
