306 LYCOPODIALES 
§ 
Fic. 154. 
Pleuromoia Sternbergt. Axis, with 
the lower part of the terminal strobilus. 
‘Two-thirds natural size. After Bischof. 
(From Engler and Prantl.) 
Scotland, has been compared by Penhallow 
with Lycopodium Selago as regards the un- 
differentiated shoot.! Without attaching too 
much importance to the last example, it 
appears certain that Lycopods, even of large 
size, existed in very early times, in which 
there was no clear differentiation of vege- 
tative and fertile regions: in fact, the 
“ Selago” condition dates back to the 
Primary Rocks. 
There can be no question of the Lyco- 
podinous affinity of the fossils thus described 
briefly in their general morphology: it 
remains then to indicate where the nearest 
correspondence is to be found between 
them and living forms. They are plainly 
related to the Ligulate Lycopodiales, and, 
being of a radial type of shoot, and usually, 
if not always heterosporous, the correspon- 
dence is nearer to the radial species of 
Selaginella: this suggests a comparison with 
S. spinulosa, from which some interesting 
points will emerge. In the first place, the 
difference of size is to be discounted: how- 
ever diverse the gigantic Lepidodendron may 
seem from the minute S. spzmulosa, the com- 
parison really relates to the relative position 
and character of the parts composing the 
plant-body. The parts which form the shoot 
—axis, folage-leaf and sporophyll, the ligule, 
and the sporangium—are identical in both 
as regards their relative positions, though 
differing greatly in their number and dimen- 
sions: in the dichotomous branching, and 
in the relation of the resulting shoots to the 
upright main axis they are alike: also in 
the dependence of the whole plant for its 
water-supply upon the base of the primary 
axis. In fact, Sedaginella spinulosa is like a 
Lepidodendran in miniature, as regards the 
scheme of its construction. The comparison 
extends also to that curious knot which is 
found at the base of the main axis in 5S. spévw/osa: here the origin of the 
roots is strictly localised: 
they appear endogenously on indeterminate 
' Canadian Record of Science, 1892, p. 8. 
