506 
PEOFESSOE W. C. WILLIAMSON ON THE OEGANIZATION 
between the two canals, in the direction of A, corresponds with a primary medullary ray 
in a Calamite ; yet we nowhere see, in the recent plants, the remarkable muriform 
arrangement of the cells common to all varieties of the latter objects. After fairly 
weighing the evidence for and against the admission of the Calamites amongst the true 
Equisetacese, as proposed by Mr. Carruthers, it appears to me that the reasons against 
doing so preponderate over those which favour such a course; to disturb generally 
accepted definitions of a living family of plants for the sake of doing this seems to me 
unwise. I should therefore propose the recognition of a distinct family of Calami- 
tacece *, which from their complex organization must necessarily stand high up in the 
great Cryptogamic division of the vegetable kingdom, which division their exogenous 
stems would directly connect more closely than has yet been done with the true Gym- 
nospermous Exogens — -a connexion which I believe will be still further strengthened 
when some other plants of the Coal-measures, especially the Dictyoxylons, have received 
a more careful study than they have yet obtainedf. 
The only question that remains for consideration is that of generic and specific nomen- 
clature. At present we have four generic names applied to Calamites, — Calamites , 
Calamodendron , Calamopitus, and Aster o-calamites. The supposed distinction between 
the first and second of these I think I have proved to have no existence ; and I doubt the 
sufficiency of the evidence, resting as it does upon a single specimen, for the recognition 
■of Professor Schimper’s genus Aster o-calamites in this list J. Nevertheless we have 
existing two very distinct types of Calamites, viz. those which have, and those which 
have not possessed the infranodal canals — a distinction that appears in every part of 
the fossil, whether it be the medullary cast or the carbonaceous investment ; hence it 
is a distinction most easily recognized in nearly every specimen that falls into our 
hands. It appears to me desirable that we should distinguish these two types by dif- 
ferent generic names. In order to avoid a needless multiplication of terms, I would 
gladly have given up my new genus Calamopitus and employed Calamites to represent 
one of the types and Calamodendron the other. But M. Beoxgxiart retains his original 
views respecting the gymnospermous nature of his genus Calamodendron , and, doing so, 
* Whilst deeming this course desirable I do not attach much importance to it, provided the accepted defini- 
tions of the natural order of Equisetaceae be sufficiently extended to embrace these fossil forms. As those defi- 
nitions now stand they exclude the Calamites. 
t The greater portion of the Cryptogamous plants of the Coal-measures, with the exception of the Ferns, 
exhibit this exogenous growth of their woody zones, thus linking them with the Exogens rather than with the 
Endogens. The arborescent form which these carboniferous Cryptogams assume affords us a better oppor- 
tunity of learning their true position in the vegetable scale than their dwarfed living representatives, none of 
which, with the exception of the Ferns, exhibit the arborescent condition. So far as the stem is concerned, we 
have in the fossil forms both the exogenous growth and the medullary rays of true Exogens ; indicating close 
affinities with that highly developed class, and between which and the cellular Cryptogams they may be re- 
garded as constituting a connecting link. On the other hand, may not the Ferns, with their detached bundles 
of vascular tissue, hemmed round and isolated by dense layers of woody fibre, connect in like manner the lower 
Cryptogams with the Endogens? — Jan. 26th, 1871. 
t It appears to me not improbable that this curious specimen belongs to Asterophyllites or to Annularia rather 
than to the true Calamites. 
