Notes . 
773 
ON A PRIMITIVE TYPE OF STRUCTURE IN CALA- 
MITES \ — Palaeontological research has afforded evidence that the 
Horsetails and Lycopods — groups now so distinct — had a common 
origin. The class Sphenophyllales, restricted, so far as we know, to 
the Palaeozoic epoch, combines in an unmistakable manner the 
characters of Equisetales and Lycopodiales, while at the same time 
presenting peculiar features of its own. Broadly speaking, it is in the 
external morp'hology and in the reproductive structures that the 
Equisetales are approached, while the anatomy has an evidently 
Lycopodiaceous character. 
The synthetic nature of the Sphenophyllales, indicated clearly 
enough in the type-genus Sphenophyllum itself, comes out still more 
obviously in the new genus Cheirostrobus. Here the general mor- 
phology of the strobilus, the form and structure of the sporangiophores 
and of the sporangia themselves, are all of a Calamarian type, while 
the anatomy of the axis is as clearly Lycopodiaceous in character. 
So far, nothing has been found to bridge the gulf which separates 
the anatomy of the Calamarieae (Palaeozoic Equisetales) from that of 
the Sphenophyllales or the Lycopods. The most ancient known genus 
of Calamarieae — Archaeocalamites — approaches the Sphenophyllales 
in the superposition of the foliar whorls and in the dichotomous sub- 
division of the leaves, points on which Professor Potonid, especially, 
has laid stress. Anatomically, however, according to the researches of 
Dr. Renault and Count Solms-Laubach, it was an ordinary Calamite, 
differing in no essential respect from those of the Coal-measures. 
The stem of Archaeocalamites , like that of its later allies, had a large 
pith, surrounded by a ring of collateral vascular bundles, the wood 
of which, primary as well as secondary, was wholly centrifugal in 
development, the first-formed tracheides lying on the border of the 
pith, at the points marked by the carinal canals. In Sphenophyllum , 
on the other hand, the whole of the primary wood was centripetally 
developed, and there was no pith. In Cheirostrobus the same holds 
good, except that an insignificant portion of the primary wood may 
possibly have been added in a centrifugal direction. In Lycopods 
there may or may not be a pith, but the whole ( Lycopodium , P silo turn, 
1 Abstract of paper read before the Botanical Section of the British Association, 
Glasgow, September, 1901 . 
3 E % 
