376 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
IL. EQUISETALES. 
The Paleozoic Equisetales, often made into a class of their own, 
under the name Calamariales or Calamariacez, were one of the domi- 
nant groups of plants at that period, attaining the stature of large 
trees, which appear to have formed an important constituent of the 
Carboniferous forests. Hence their organization was in various re- 
spects on a higher level than that of their recent survivors, repre- 
sented by the genus H'quisetum, at the same time, allowing for these 
Fic. 2.—Cheirostrobus Pettycurensis. Diagram of cone, the upper part in transverse, the 
lower in radial section. In the transverse section, six sporophylls, each showing three 
segments, are represented. Sp. a., section in plane of sterile segments; Sp. b., section 
in plane of sporangiophores; st, lamina of sterile segments; f, lamin of sporangio- 
phores; sm, sporangia; v. b., vascular bundles supplying sporophylls; Aw, axis; cy, 
stele. The longitudinal section shows the sporangiophores and sterile segments in their 
relation as ventral and dorsal lobes of the sporophylls; lettering as before. 
adaptive differences, the structure of the Calamariacee had very 
much in common with that of our familiar Equisetacee. 
Even in habit there seems to have been a considerable resemblance 
to recent forms. The leaves were always in whorls, and usually of 
simple form and comparatively small size, though not so reduced as 
in Equisetum itself. In the oldest known Calamarian, however, the 
Devonian and Lower Carboniferous genus Archwocalamites, the 
leaves were often dichotomously compound, thus showing an inter- 
