Pteridosperms and Angiospenns. 237 
series as being in somewhat different phases of evolution or as 
having responded to the stimulus of spore- (or even seed-) pro¬ 
duction in a rather different way. 
The Lycopsida in the cryptogamic condition seem to have 
undergone marked adjustment and specialisation in connection with 
the spore-bearing function, for a parallel to which, in the Pteropsid- 
series, one has to turn to fairly advanced spermophytes such as the 
Cordaiteae and Cycadophyta. 
The Lycopods and Calamites reached their zenith in Palaeozoic 
times, when they attained the dimensions of forest trees. For 
some reason or another they seem to have exhausted their resources 
of adaptation upon the cryptogamic method, so that they were 
without the needful reserve of plasticity to follow up the beginnings 
of seed-production upon which some of their representatives are 
known to have stumbled (Lepidocarpon). 
The megaphyllous forms, on the other hand, behaved in a 
different way. To them the cryptogamic state was not a phase 
upon which to expend themselves. They retained their full plasticity 
till the supreme moment of becoming seed-plants, and only then, 
and without hastening, did they begin to modify and specialise their 
organs of fructification. 
As an illustration of the remarkable adjustment in matters of 
sporangial details of which palaeozoic Lycopods were capable, the 
cones known as Spencerites and Lepidostrobus, respectively, may be 
taken. The former is remarkable for the distal attachment of the 
sporangium to the sporophyll, where it is inserted upon a cushion 
which has been compared with a Sphenophyllaceous sporangiophore. 1 
In Lepidostrobus, on tbe other hand, the radially elongated 
sporangium is attached throughout its length to the upper surface 
of the pedicel of the sporophyll. This difference—not improbably 
of nutritive significance—offers some analogy with the relations of 
nucellus and integument in the two groups of Pteridosperms: 
Neuropterideae and Lyginodendreae. In the former the nucellus 
stands free within the integument ( Trigonocarpon , Stephanospennum), 
whilst in the Lyginodendreae ( Lagenostoma ) a large measure of 
coalescence obtains, so that only the tip of the nucellus is free, a 
condition also found in living Cycads. The free condition is 
presumably the more primitive, and in this connection it would be 
of some interest should Spencerites turn out to be the cone of 
1 D. H. Scott, loc. cit., p, 170. 
