Equisetales . 
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II.—EQUISETALES. 
The first order contained in the phylum of the Equisetales, 
the Calamariae, consists only of fossils. The sterns, marked 
externally with longitudinal ribs, show in transverse section a circle 
of woody bundles, separated by medullary rays and surrounding a 
pith. The remains of the protoxylem are distinguishable in a canal on 
the inner edge of each bundle, known as the carinal canal. The 
primary xylem was thus centrifugal, and beyond it secondary 
centrifugal xylem was also formed. Until 1901 it was generally 
thought that the xylem of Calamarian stems was wholly centrifugal, 
and that the protoxylem abutted on the pith ; but in that year Dr. 
Scott described a stem to which he gave the name of Catamites 
petty cur ensis, in which there is a considerable amount of centripetal 
xylem between the carinal canal and the pith (13). Owing to the frag¬ 
mentary condition of the fossil it has been impossible to ascertain 
whether it belonged to Archaeocalamites or Catamites. Its discoverer 
considers its structure as primitive ; the principal reasons for such 
a supposition are that there is, as will be shown later, good evidence 
that the Equisetales had a common origin with the Sphenophyllales, 
that there is some evidence of their common origin with the 
Lycopodiales also, though at a more remote period, and that in 
these two phyla the primary xylem was probably primitively 
entirely or largely centripetal. The antiquity of the fossil (it comes 
from the Calciferous Sandstone, a series of rocks occurring at the 
very base of the Carboniferous system) favours Dr. Scott’s view, 
which is also supported by Professor Bower (2) and which few, if 
any, botanists would dispute. 
In Archaeocalamites the vascular bundles and therefore the 
ridges on the stem were superposed at the nodes ; in Catamites they 
alternated. Archaeocalamites appears in the Mid-Devonian, and is 
most abundant in the Culm, dying out at the very base of the Coal 
Measures (9); Catamites appears to have attained its maximum 
development in the Middle and Upper Coal Measures (9). Thus the 
former genus appears to be, on the whole, more ancient than the latter, 
and it is probable that the course of the vascular bundles in Catamites 
arose by the modification of the type of course found in Archaeo¬ 
calamites. This appears to be Professor Seward’s view, as the 
