Lycopodiaceous Cones from the Lower Coal Measures . 391 
portion of the sporophyll. The ligule is set in a deep ligular pit, and 
is somewhat large when compared with its condition in Lepidostrobus. 
It is suggested that the type of sporophyll represented by Bothroden - 
dr on mtmdum , the male Miadesmia , and Selaginella is a close copy of 
a very early Lycopodiaceous type. Lepidostrobus would be derived from 
a cone having sporophylls of this type, on the adoption of an arboreal habit 
by the heterosporous Lycopods, because radial elongation of the sporangium 
is the most economical way of increasing the number of spores produced, 
a necessity for a large tree. 
If this elongation takes place in the part of the sporophyll between the 
axis and the insertion of the sporangium, we arrive at a condition much like 
that of Spencerites, and from that condition we can pass through Mesostrobus 
to Lepidostrobus. 
The fact that two branches of one stock, differing in important charac- 
ters, tends to follow similar courses during their evolution is one very 
strongly borne in on students of Palaeozoology, and it is suggested that 
a similar parallelism is to be found between the homosporous and the 
heterosporous Lycopods ; and that Spencerites , which is probably homo- 
sporous, has been derived from a cone resembling that of Bothrodendron 
mundum , in consequence of that increase in size of the homosporous stock 
which we see in the genus. 
The peculiar feature of the Spencerites cone, the peltate expansion 
of the horizontal portion of the sporophyll between the sporangium and the 
lamina, is to be regarded as having a utilitarian purpose, that of affording 
protection to the very weakly attached sporangium. It is further pointed 
out that the idea that Spencerites is an ancient and archaic type rests 
entirely on the assumption that the * ventral hump ’ is derived from a 
sporangiophore homologous with that of Sphenophyllum Dawsoni , and 
on the further assumption that the Lycopods in general are derived from 
a Sphenophyllaceous or proto- Sphenophyllaceous ancestor. It is pointed 
out that the evidence in favour of this view is really extremely slight, 
although there is also not much against it. 
I wish to express my thanks to Prof. F. E. Weiss and Dr. W. E. Hoyle 
for allowing me to describe the unique series of sections of Mesostrobus 
now in the Manchester Museum. 
I hear from my friend Mr. W. T. Gordon that he has a cone showing 
similar morphological characters from the petrified plant material of lower 
carboniferous age at Pettycur. I look forward with interest to his de- 
scription of this cone. 
