SPORE-PRODUCING MEMBERS 325 
sub-genus /hopalostachya, while in the simpler Se/ago-forms the sporophylls 
are as in LZ. Brownz, or, better still, in Pinakodendron. The wall of the 
mature sporangium is frequently represented by the single prismatic outer 
layer alone, the inner thin-walled layers seen in Z. Brownt? being absent : 
this difference is comparable to that seen in Lycopodium, where the mature 
wall usually consists of a single layer, but. in Z. adichotomum of several 
layers. There is also some 
divergence in detail of the 
internal upgrowths from the 
basal ridge: in most Lefz- 
dostrobi these take the form 
of longitudinally disposed 
plates, of which one or more 
project upwards into the 
sporangial cavity. Lastly, 
there is the fact of hetero- 
spory, which has now been 
established in a number of 
examples, though it must 
not be assumed for them all 
without actual demonstra- 
tion. Such differences as 
those mentioned are, how- 
ever, of secondary impor- 
tance, and in the general 
morphological character of 
the Lepidodendroid cones 
there is substantial unifor- 
mity as regards the relation of 
sporophyll and sporangium, 
as well as in their form. 
The fructifications of 
Sigilaria appear as cones 
sometimes sessile, but more ,Zifidestyaius Velttrinianus. Longitudinal section of con, 
commonly bore on long 27 9 que, slew sels a, an! estas passing put to 
latetal- Deanenes, Wileh: are 7s aie ee eneees, abana dy Rani Rebs 
covered below with acicular 
bracts: such strobili are thus more strongly differentiated from the 
vegetative axes than is the case in Lefzdodendron. The plan of construction 
of the cone itself appears to have been the same, and though its preservation 
is commonly imperfect, it seems that the sporangia of Sve7//aria resembled 
those of Lepidodendron in their form and mode of insertion, as also in the 
existence in them of a heterosporous condition. They were sometimes of 
large dimensions: frequently, however, of smaller size. Among them a 
small cone, described by Zeiller as Sig7//ariostrobus Crepini, differs from 
