GENERAL MORPHOLOGY 303 
widely spreading system: from these the rootlets radiated in all directions, 
developing to a length of a foot or more, and showing dichotomous 
branching. The underground system was thus proportional to that above 
ground. In the Sigillariaceae similar trunks are found, but it seems 
doubtful whether they show the same constancy of initial type as in 
Lepidodendron. In Pleuromora the base of the upright stock swells into 
a tuberous body, which is very Svigmaria-like in the fact that it is 
covered by root-scars, while it extends into four blunt processes corre- 
sponding in position and character to Stigmarian trunks, though much 
shorter (Fig. 151). It would 
seem probable that in this 
relatively late Triassic fossil 
(which is unfortunately known 
only in the form of casts, 
not structurally), a simple 
representative of the Lepido- 
dendroid basal region is cor- 
rectly recognised. In all of 
the dendroid forms the Stig- 
marian trunk appears to have 
been present, as a basis for 
the roots: but the latter were 
not restricted to that position: 
Potonié shows how the scars 
of their insertion may be 
sometimes found on the leaf- 
bearing axes also, associated 
with some degree of regularity 
with the leaf-scars.! ieee 
The leaves of the fossil 
Pleuromoia Sternbergit. Swollen base of stem with root- 
. ‘ : scars, and showing part of the aerial stem, with the epidermis 
Lycopodiales were sometimes and leaf-scars on the right, and on the left the sub-epidermal 
of considerable size, but un- sculpture. (After Bischof, from Engler and Prantl.) Two-thirds 
2 natural size. 
branched and of simple form. 
They expanded at the base into the well-known cushions, which in many 
forms occupy the whole external surface of the axis: this corresponds to 
what is seen among the living Lycopods. On the upper surface af the 
leaf, near its base, the ligule is seated: it appears to have been a constant 
feature in the dendroid Lycopodiales, and the occurrence of it links them 
rather with Se/agine/la than with Lycopodium. It was often seated in a 
deep pit—as it is in some living Selaginellas—and this pit persists as a 
marked feature in the neighbourhood of the leaf-scars, whenever the cast 
of a stem-surface is well preserved (Fig. 152). 
The vegetative region appears to have been, as a rule, purely 
vegetative: the sporangia are restricted to well-defined cones or strobili, 
1 Lehrbuch der Phlanzenpalacontologte, p. 212, Fig. 215. 
