ON THE INTERNODES OF CALAMITES. 491 
Note on the Internodes of Calamites. Ву Prof. Percy Овом, M.A., D.Sc., 
F.L.S. With some Observations by F. J. Lewis, D.Sc., F.L.S. 
(With 4 Text-figures.) 
[Read 7th March, 1912.) 
SEVERAL botanists * have supplied records of Calamite-stems showing the 
recurrence of short internodes separated by a number of longer ones, and 
Williamson drew special attention to such a recurrence at intervals of eight 
and five internodes respectively in two specimens. One feature worthy of 
note is that in a number of specimens the branch-scars are inserted 
exclusively in contiguity with these short internodes. Horwood (loc. cit.) 
points out that the gradual increase of length of the successive internodes, 
commencing at one of the short ones, is paralleled by similar features in the 
stems of modern Equiseta. 
So far no explanation of this rhythmic succession of internodes on 
Calamite-stems has been offered, except the teleological one presented by 
Horwood, according to whom “the short internode appears to serve the 
purpose of imparting additional strength to the stem owing to the weight of 
branches above.” This explanation, so far as I understand it, is placed 
out of court not only by the occurrence of similar characters in bamboos 
and dicotylous plants, in which the branching is not necessarily correlated 
in position with short internodes, but also by Horwood’s observation that 
Equisetum sylvaticum and Е. litorale display a similar internodal periodicity— 
for in these two species branches occur at all cauline nodes. 
Modern Angiospermz seem to supply the answer to the problem, for in 
them, so far as is known, each rhythmic cycle of internodes in the vegetative 
region of the stem corresponds to the increment in length of this during a 
single growing season ; and normally there is one such season in each year. 
It is necessary to note several features concerning the rhythm of these 
plants, if they are to be used as evidence in regard to Calamites :— 
1. The internodal rhythm of modern dicotyledons, though liable to some 
disturbance by external factors, is of regular type and more or less charac- 
teristic of the species, as is best shown graphically by means of an internode- 
curve f. In at least a great number of species the successive internodes 
* For literature see: A. R. Horwood, * On Calamites Schützei, and on the Correspondence 
between some new features observed in Calamites and Equisetacee.” Journ, Linn. Soc., 
Bot. vol. xxxix. 1910, pp. 277-89; W. Jongmans: “ Beiträge zur Kenntnis von Calamites 
undulatus, Sternb.” Med. v.s Rijks Herbarium, Leiden, 1911, pp. 43-59. 
+ Percy Groom: * Longitudinal Symmetry in Phanerogamia.” Phil. Trans. London, 
В. vol. 200, 1908, рр. 57-115; “ The Longitudinal Symmetry of the Centrosperme.” Trans. 
Linn. Soc, ser. 2, Bot. vii. 1909, pp. 267-302 
