296 LYCOPODIALES 
approaches Z. Se/ago in its alternation of successive sterile and _ fertile 
zones. On such grounds the ézwndatum group has been associated with 
Phlegmaria by Baker in the sub-genus Zef/dotis, though this association 
is not now upheld. In the rest, however, the 
definition is more exact, and is strictly main- 
tained; for instance, in Z. cernuwm in a very 
large number of specimens a transition from 
the strobilus back to the vegetative shoot was 
never observed. The same is the case in the 
species associated as the group of ZL. clavatum, 
which are terrestrial trailing species, with well- 
defined strobili. In this series the intercalation 
of a peduncle, with small distant scales, between 
the larger-leaved foliage shoot and the definite 
strobilus is indicated (Fig. 144). The question 
whether the peduncle is directly derived from the 
basal part of the strobilus, or from a specialised 
part of the already sterile foliage region, may be 
left open; but as sporangia are not found on it, 
nor even any vestiges of arrested sporangia, the 
latter seems the more probable source of the 
peduncle: the biological importance of it in 
ground-growing forms is readily understood. 
Finally, the dorsiventral species, previously 
grouped as the sub-genus Diphasium, are now 
distributed according to their obvious affinities ; 
the dorsiventral character of their vegetative 
shoot being held as a secondary adaptation: 
the strobilus, however, remains as clearly defined 
as in the more advanced representatives of the 
sub-genus /hopalostachya, and does not share in 
the dorsiventral development. 
A comparison of the living species of Lyco- 
Fic. 144. podium thus appears to demonstrate a progression 
Lycopodium carolinianum, L. from a less differentiated to a more differentiated 
A=figure showing habit. About Fi 
two-thirds natural size. #=stro- State. In the simplest forms the whole of the 
bilus. Natural size. C=sporophyll 5 
seen from above. x6. Dethe unbranched or sparsely-branched shoot is practi- 
Se et ea ce cally a fertile strobilus, which serves the double 
. purpose of assimilation and of spore-production. 
By gradual steps the living species suggest how the two functions became 
separated: a purely vegetative region was established by abortion of the 
sporangia, and it was naturally located in the first-developed or lower part 
of the plant, since the function of nutrition must necessarily precede that 
of spore-production. The fertile upper region also became more specialised, 
and in the species where it is most clearly defined from the vegetative region 
