388 Watson . — On Mesostrobus, a New Genus of 
It is quite safe to assume that the early homosporous cone did not 
differ much from the heterosporous cone which had just branched off from 
it. The causes which led to the production of Lepidostrobus , on the increase 
in size of the heterosporous Lycopods, would in a precisely similar manner 
tend to produce a similar effect on the cones of any homosporous Lycopod 
which similarly increased in size. 
The whole would be an illustration of the Doctrine of Rectigradation. 
Hence, it seems possible to explain Spencer ites as a stage in the production 
of a Lepidostrobus on the homosporous side, which has been prevented from 
going on, by the development of a new method of protection, by an out- 
growth of the sporophyll just to the outside of the sporangium. This 
protection would be needed to make amends for the weak mechanical 
attachment of the sporangium, and might begin as a small lump and carry 
the attachment of the sporangium up with it. 
If Spencerites is secondarily derived from a homosporous cone resem- 
bling that of Bothrodendron mundum , we should expect to see vestiges 
of its ancestry. Two characters can. I think, be interpreted as such. 
On reference to Scott’s original description (Scott, ’97), PI. XIV, Fig. n, 
a figure of a radial section of two sporophylls of Spencerites insignis shows 
that the course of the trace is not straight through the sporophyll, but that 
in the region of the proximal part of the peltate head, the trace takes 
a little loop downwards and then comes up again. 
Miss Berridge’s restoration (’05) does not show this, but apparently the 
trace is not shown in this region in her radial section. 
I have been able to see this arrangement (only very badly) in tan- 
gential section Q. 489 in the Cash Collection of the Manchester Museum, 
from Halifax, and it seems to me to be natural, although it may not be 
always present. 
This loop is, it seems to me, quite comparable, and in fact homologous 
with the loop round the base of the ligule in Bothrodendron mundum 
and Mesostrobus. It may be objected that the loop is rather nearer the 
axis than would be expected on this view ; in answer to this I would point 
out that in Lepidostrobus it is further out, and no longer embraces the base 
of the ligule. 
This loop suggests that the ligule is possibly included in the ‘ ventral 
hump ’, a suggestion which has, I believe, been already made by Miss Ber- 
ridge. In the Lycopods generally, the ligule is a very definite organ 
well marked off from its base, so that not very much weight should be laid 
on this suggestion. 
Miss Berridge in her paper on Spencerites shows that the trace in 
passing from the outer cortex to the sporophyll rises slightly above the 
base and then comes down to enter it. This arrangement is exactly similar 
to that which occurs in Mesostrobus and probably in Bothrodendron mundum. 
