GENERAL MORPHOLOGY 309 
potentially a fertile strobilus, in which the vegetative and reproductive 
systems are not differentiated from one another. This, together with its 
prevalent absence of terminal branching, points out Jsce/es as a near 
approach in its general construction to the strobiloid type theoretically 
primitive for the Lycopodiales: this it shares with the simplest Se/ago- 
forms of Lycopodium. But it is with the dendroid Lycopodiales that 
Lsoetes shows common characters of the sporangia themselves: there is 
also some similarity to them in the structure of its abbreviated but bulky 
stock: on this also the very similar bifurcating roots are inserted, but in 
Zsoetes their origin is localised in the depressed grooves which traverse 
the stock longitudinally, instead of their being borne on Stigmarian out- 
growths, as in the fossils. The JZsoefes plant is then like a partially 
differentiated Lep~zdostrobus seated upon a Lepidodendroid base: in fact, 
like a stunted ZLefsidodendron,, with its preliminary vegetative phase very 
short. Its mature shoot still carries on both vegetative and propagative 
functions, and in this lack of differentiation a primitive character is to be 
recognised. 
The account thus given of the general morphology of the mature 
sporophyte in the Lycopodiales, living and fossil, shows the essential 
identity of their plan of construction throughout the phylum, and how in 
the two series, the ligulate and the eligulate, parallel conditions of differ- 
entiation are represented. In both the structure of the shoot is essentially 
strobiloid, with a constant numerical relation of the sporangium to the 
subtending sporophyll. In both series the branching of the axis is primarily 
by dichotomy, with a deviation in the more specialised types, and especially 
in the higher ramifications to the monopodial branching: but in certain 
simple types branching is rare, or even absent. The shoot is fixed in the 
soil by roots, formed chiefly, or even exclusively, at the base of the axis 
in the simpler types; but in the more specialised they may be formed at 
various other points on the shoot-system, or on outgrowths from it of an 
indeterminate character. In both series there is evidence of abortion of 
sporangia, leading to a segregation of definite tracts of the shoot-system 
devoted to nutrition and to propagation respectively: in the higher types 
the strobilus becomes a definite cone of limited growth, clearly marked 
off from the lower’ vegetative region: the production of spores is thus 
deferred in the individual life, and a more lengthy _vegetative phase 
intercalated before that event. This progressive differentiation is best 
illustrated in the eligulate series, which is also the more primitive in 
respect of its homosporous condition. We are thus led by comparison 
of the Lycopodiales, living and fossil, to contemplate as a fundamental 
type of their shoot a simple unbranched strobilus with unlimited 
apical growth, bearing undifferentiated leaves, and having one sporangium 
associated with each leaf. This may not improbably have been the 
primitive type from which, by branching, by formation of a root-system, 
by differentiation of the sterile from the fertile region, and, finally, by 
