302 LYCOPODIALES 
borne by the megasporophyll. So far as it goes, then, the evidence from 
the fossils favours the conclusion that plants resembling Se/agzne//a existed 
in the primary rocks, and that even the more specialised heterophyllous 
type of Selaginella dates at least from the Carboniferous period, while 
it seems possible that a seed-like habit had already been established. 
‘The dendroid Lycopodiales are among the earliest known fossils, 
dating from the Lower Devonian period to the Trias. They include the 
families of the Lepidodendraceae, Bothrodendraceae, Sigillariaceae, and 
Fic. 150. 
Ground plan of a Tree-stump with Stigmaria-trunks. One-sixtieth the natural size. 
(After Potonié.) 
Pleuromoiaceae. Underlying the differences of detail according to which 
these families are distinguished, there is a general unity of morphological 
plan: the essential features of it are as follows. The main axis was 
upright, rising in some cases to a height of 100 feet. It was bulky 
relatively to the numerous simple leaves which it bore: it branched 
upwards in a dichotomous manner, in most cases profusely: in some of 
the Sigillariaceae, however, and in Fleuromotia branching may be entirely 
absent. The development of the branches of the dichotomy were in 
various cases either equal or unequal, a fact which leads to differences of 
habit, as is seen to be the case in Lycopodium or Selaginella. The axis 
was fixed in the soil by a shallow and broadly spreading system of 
Stigmarian trunks (Fig. 150). In Lepedodendron the main Stigmarian 
trunks usually numbered four, which bifurcated repeatedly, thus forming a 
