192 Lady Isabel Browne. 
and form alternating zones, or finally in L. compaction and L. 
Trencilla all the leaves of the mature plant appear to bear 
sporangia (6), (7). It is generally conceded that the forms without 
definite cones are the more primitive, whether on account of the 
absence of differentiation of the sporophylls from the sterile leaves 
or of the sterile leaves from the sporophylls. Professor Bower, 
being a strenuous supporter of the antithetic origin of the 
sporophyte, holds that the vegetative leaves are sterilized sporo¬ 
phylls and that the most primitive type is therefore that of L. 
compaction, where every leaf, or at least every leaf persisting on 
the mature sporophyte bears a sporangium. The question of the 
the antithetic or homologous origin of the sporophyte cannot be 
considered here, but the enormous age of the vascular sporophyte 
and the presence of Lycopods with a large vegetative system in 
the Devonian, or perhaps even in the Silurian, renders it unlikely 
that L. compaction and L. Trencilla should have retained to the 
present day the hypothetically primitive condition of a sporophyte 
fertile throughout. Other species all have sterile basal regions, 
sometimes of considerable length. In the present condition of 
our knowledge, neither the homologous nor the antithetic origin of 
the sporophyte can be regarded as proved, or even probable. In 
view of the fact that all known Palaeozoic forms of Lycopods were 
provided with sterile leaves (except Spencerites, the cone of which 
alone is known, bearing small bracts below the region of the 
sporophylls), and that in many of them the vegetative system 
attained to tree-like proportions, it would seem more natural to 
regard the complete fertility of the sporophyte of certain species of 
Lycopodium as probably secondary, and possibly due to the 
reduction of the vegetative part of the plant. The Lycopodiaceae 
are certainly very primitive plants, for since the removal of the 
Psilotaceae from this phylum they constitute the only homosporous 
order. Perhaps, therefore, the want of differentiation between 
leaves and sporophylls and the non-strobiloid condition of certain 
species of Lycopodium may be primitive characters. In Lycopodites 
Stockii the sporangia were borne on sporophylls, aggregated into 
cones, but these were not sharply defined below and some of the 
leaves below the cone bore sporangia (7). The discovery of a tree¬ 
like Lycopod without a definite strobilus ( Pinakodendron ), and of a 
non-strobiloid herbaceous plant apparently very close to Selaginella 
(Selaginellites elongatus) (12), renders it not improbable that the 
earliest members of the Lycopodiales began to diverge from the 
