Mesoxylon Lomaxii and M. poroxyloides. 1027 
relatively large dimensions and distinct mesarch structure of those primary 
xylem-strands which are about to pass out from the pith, while the same 
strands, lower down in their course, are reduced in size, and in some cases 
assume endarch structure, owing to the dying out of the centripetal xylem. 
A single strand passed out from the pith to form the leaf-trace. 1 
The really characteristic point in Calamopitys is the presence of the 
quite peculiar large, round mesarch xylem-strands, which are unlike those 
of any other plant I have seen. Their structure in C. Saturni and C. fasci - 
cularis (to take an example from each group) is identical, as I hope to show 
more in detail on another occasion. The only differential character of any 
weight between Calamopitys and the new Eristophyton is the width of the 
medullary rays, which are generally wide in the former and narrow in 
the latter. This, however, appears to be inconstant, for, in a section 
of C. annularis , very kindly lent me, among many other preparations, 
by Count Solms-Laubach, the rays are only one or at most two cells in 
width, thus differing from the pluriseriate rays usual in C. Saturni and even 
in other specimens of C. annularis. There is no reasonable doubt that the 
species of Calamopitys described by Count Solms-Laubach were Pterido- 
sperms, as indicated by their Kalymma petioles. The important question 
at issue between Dr. Zalessky and myself is whether the species C. fasci- 
cularis and C. Beinertiana were likewise Pteridosperms, or belonged to 
a higher group. This goes much beyond the mere question of generic 
separation, which is of secondary importance. 
At present I must adhere to my view that the agreement in the 
primary characters of the wood, between the species placed by Dr. Zalessky 
in Eristophyton and the type species of Calamopitys, is so close as to prove 
a very near affinity. The question will not, however, be finally decided 
until the cortex and leaf-bases of the former species are known. 
One argument used by Dr. Zalessky must be shortly dealt with, 
as it appears to me somewhat misleading (Zalessky, ’ll 1 , p. 27). He says 
that, if my view is just, we must suppose that the species fascicularis and 
Beinertiana had fern-like foliage. He regards his Callixylon Trifilievi as 
certainly allied to these species. He finds reason to believe that the latter 
plant may have had a stem reaching about a metre in diameter, and thinks 
it improbable that such trunks could have borne the foliage of a Fern. 
Now, to begin with, Callixylon Trifilievi shows no close affinity to 
Calamopitys fascicularis and Beinertiana. It is practically a Pitys, and no 
one has attributed filicoid foliage to Pitys, which was more probably of 
Cordaitean habit. Secondly, there is no reason to doubt that in Palaeozoic 
days stems of great girth bore fern-like foliage. A specimen of Medidlosa 
stellata discovered by Weber (Weber und Sterzel, ’ 96 , p. 25), though 
decorticated, measured nearly a metre (48 x45 cm.) in diameter. It is 
well known that the foliage of Medullosa was fern-like (e. g. Neuropteris, 
