54 
M. G. Sykes. 
sporangium from the main axis in L. selago may be merely a con¬ 
trivance to save time ; perhaps the fact that even here it does not 
appear to be formed from leaf tissues may have some connection 
with the morphological question as to whether the sporangium 
is derived from tissues of axial or foliar nature 
The series of species constituting the genus Lycopodium is far 
more easily interpreted as a reduction than as an elaboration series. 
(I.) For, if the simpler species are primitive, it is difficult to 
understand the evolution of a stalked sporophyll with a dorsal flap, 
adapted for the protection of a distally-placed sporangium, whilst 
bearing its sporangium in an axillary position. Yet such is the 
state of affairs in L. inundatum, and it is easily explicable on the 
other hypothesis, by which the lax arrangement in L. selago arose 
from a compact cone like that of L. cernuum by a series of steps 
involving the gradual loss of specialised adaptions. For then, we 
have in L. inundatum an intermediate step, in which the dorsal 
protective flap is still present, but is no longer perfectly effectual, 
since the sporangium is now not in a distal position on the sporo- 
phyll. 
(II.) Again the positions of the line of dehiscence in the 
various sporangia support the second view. A longitudinal section 
of L. inundatum, such as that drawn in Text-fig, 5, VII., shows 
that the spores are liberated opposite the space between the distal 
ends of two sporophylls. But the sporangia are not completely 
enclosed as in L. cernuum, and are exposed between the proximal 
ends of the sporophylls, so that the necessity for this mode of 
dehiscence is not clear here and is still less obvious in L. volubile, 
where there is not even a dorsal flap to the sporophyll. I think 
the displacement of the line of dehiscence is best explained in these 
two species as a reminiscence of the more complex cones in which 
it was really important, in order to ensure dissemination, to 
liberate the spores in a lateral position. 
(III.) The appearance of the lignified cells at the base of the 
sporangium in L. cernuum so forcibly recalls vascular tissue that 
one cannot resist the temptation to regard them as primitively 
vascular in origin. Though of course it is true that the 
development of vascular tissue cannot be brought forward as evidence 
of undoubted phylogenetic value, yet these lignified elements 
are of especial interest in this species, coupled as they are with 
the existence of a well defined parichnos in the sporophyll. The 
lignified cells in L. inundatum, the walls of which are exactly 
