326 LYCOPODIALES 
the rest in the distal insertion of the sporangium upon the sporophyll, 
corresponding. in this respect to Spencerites. 
Taking a general view of the fructifications of the Lycopodiales, the 
most salient feature is the constancy of the numerical relation of sporan- 
gium to sporophyll. In the whole phylum of the Lycopodiales each 
sporangium is subtended by its sporophyll, while the median planes of 
both those parts coincide. In most cases the sporangium is in close 
proximity to the axis, or it may even be inserted upon it: gccasionally 
its position is further removed from the axis and inserted towards the 
distal end of the sporophyll: these differences are of secondary importance 
so long as the median position is regularly preserved. It is to be noted 
that such extreme conservatism in number and in place of the sporangia 
is peculiar to this phylum of Vascular Plants, in which also the closest 
relation exists between the sporangia and the axis: in all other types 
the sporangia show not only a less close relation to the axis, but also 
less definiteness in number and in position: there is often, indeed, some 
rough proportion between the size of the appendages and the number of 
the sporangia which they bear. 
The type of the sporangium itself is constant, though liable to differences 
in proportion: it is always more or less fan-shaped in tangential section, 
but the angle of spread of the fan is liable to considerable variation. It 
is, however, in the extension radially outwards from the axis that the 
greatest differences of proportion are seen, and it has been shown above 
that in the living species of Lycopodium the differences may be correlated 
with the degrees of differentiation of the strobilus from the vegetative 
region; the narrow compressed form of sporangium with relatively thin 
stalk is found in the less differentiated, the sporangium more radially 
extended with short thick stalk in those with more clearly differentiated 
strobili. The extremes ofgradial extension are seen in the dendroid fossils, 
as well as in Jsoefes. It would seem probable, as suggested by the com- 
parative study of the living species of Lycopodium, that the larger sporangia 
are derivative types, and that the enlargement was consequent upon 
increased facilities of nutrition: such increased facilities are afforded by 
the large size of the assimilating leaves in Jsvefes; but in the more 
differentiated species of Lycopodium, and in still higher degree in the 
dendroid fossils, by the extensive vegetative system which precedes the 
production of cones. The abortion of sporangia, and consequent reduc- 
tion of their number in proportion to the foliage leaves, would tend in 
the same direction. Such circumstances would encourage enlargement 
of the spore-output, which is most readily and directly secured by increase 
in size of the individual sporangium in so hide-bound a type as that of 
the Lycopodiales. The extreme enlargement led to mechanical and 
nutritive difficulties, which were met, perhaps independently, in Jscezes 
and in some Lepidodendrons by the formation of trabeculae: these origi- 
nated in /sve¢es by partial sterilisation of sporogenous tissue. But though 
