280 THE AMERICAN NATURALIST. [VoL. XXXIX. 
The hollow jointed stem, the remarkably regular apical growth 
of both shoot and root, and the structure and arrangement of 
the vascular bundles are very different from the lycopods with 
which it has been attempted to connect the Equisetales. It is 
true that both the latter class and the lycopods are characterized 
by relatively small leaves, but their structure and relation to the 
shoot are very different in the two classes. 
It may be questioned whether the excessive reduction of the 
leaves found in most species of Equisetum is not a secondary 
condition. The oldest known type, Archzocalamites, while 
agreeing closely in its general structure with Equisetum, dif- 
fered in the very much better developed leaves, which not only 
were much larger than those of Equisetum, but were repeatedly 
branched in a dichotomous manner, more suggestive of the 
leaves of certain ferns than of any forms among the lycopods. 
Their relation to the shoot, however, was precisely that of 
the existing forms. The peculiar extinct order, the Spheno- 
phyllales, which are admittedly of equisetaceous affinities, also 
possessed dichotomously divided leaves, or wedge-shaped leaves 
with dichotomous venation. 
The fact that both Equisetales and lycopods have the spo- 
rangial structures arranged in a strobilus or cone, can hardly be 
taken as a necessary indication of relationship. The structure 
of the cones in the two classes is very different, the sporangio- 
phores of Equisetum being hardly comparable to the true spo- 
rophylls of Lycopodium. Moreover, true strobili are known in 
the fern series, as shown by the cycads, whose relationship with 
the ferns is now almost universally admitted. : 
While the structure of the sporangia and of the spores is 
extremely characteristic in Equisetum, the development of the 
sporangium is much more like that of the eusporangiate ferns 
than like that of any of the Lycopodinez. 
Jeffrey lays much stress upon the arrangement of the vascu- 
lar bundles in Equisetum, which he thinks can be compared 
better to those of the Lycopodiales than to those of the ferns. 
Van Tieghem,! on the other hand, refers Equisetum to his 
l Traité de Botanique. 
