380 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
ported by additional characters sufficient to indicate real relationship 
rather than mere analogy. 
Professor Thomas considers that we are justified in including the 
Psilotacee in the class Sphenophyllales, and in this he is followed 
by Professor Bower in his latest works. If we were compelled to 
choose between Sphenophylales and Lycopodiales, I should certainly 
incline to the former. alternative, as expressing the nearer affinity, 
but the differences between Psilotaceze and the Paleozoic plants which 
have hitherto constituted the class Sphenophylales seem to me too 
great to render a union under the same name desirable. The most 
obvious difference, of course, is the phyllotaxis, spiral or at least 
scattered in the Psilotaceze but verticillate in the Sphenophyllales. 
From the great constancy of this character throughout the groups 
included under Articulatee I am inclined to attach considerable im- 
portance to it. Further, on present evidence, the mode of branching 
seems also to mark a distinction between Psilotaceze and the Spheno- 
phyllales, dichotomy of the stem occurring in the former, but not, 
so far as we know, in the latter. For these reasons I prefer to treat 
Psilotum and Tmesipteris as forming a class of their own, the Psilo- 
tales, having most in common with the Sphenophyllales, though not 
wholly without the Lycopodiaceous affinities which have hitherto 
been attributed to them. 
IV. LyYCoPopIALES. 
As is well known, the Lycopods of the Paleozoic period formed 
one of the dominant groups of plants, as shown by the great number 
both of species and individuals, the lofty arboreal habit of most of 
them, and the high organization which they attained. While the 
best known representatives, the Lepidodendres, were trees, reaching 
a height of 30 meters or more, there is evidence for the contemporary 
existence of small herbaceous plants, resembling the Club mosses of 
the recent flora. The extensive genus Lepidodendron, which we may 
take as typical of the class, ranges from the Devonian to the Permian. 
The species were trees, with a tall upright shaft bearing numerous 
dichotomous branches forming a dense crown, and clothed with 
numerous long and narrow simple leaves, ranged in a complex spiral 
or verticillate phyllotaxis. When the leaves were shed, their bases 
remained on the stem, and the sculpturing which they present affords 
the external characters by which the “species” are commonly dis- 
tinguished. The markings on the leaf cushion and scar are de- 
scribed in all the text-books and need not detain us here. In habit 
the Sigillarias must have been peculiar, for the stem appears to have 
branched but sparingly, or even, in some cases, not at all, the long 
upright trunk terminating, ike a Xanthorrhewa, in a sheaf of long, 
grass-like leaves. The leaves were usually arranged in conspicuous 
