ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 879 
As sub-types we have: 
B 1. The change takes place suddenly, the interfascicular wood at once 
extending across the whole width of the ray. 
B 2. It takes place gradually, the ray becoming narrowed and sub- 
divided by the formation of new strands of trachez, both at the 
sides, and in the middle of the ray. 
The sub-type A 1 is exceptional among our specimens. We have examined stems* 
with wood about eighteen elements in radial section, in which the rays are certainly 
parenchymatous throughout and do not diminish in thickness. ‘Tangential sections 
of this type of stemt leave no doubt of the purely parenchymatous structure of the 
principal rays. In no case, however, is the stem of any considerable age, so we 
cannot be certain that the condition is anything more than a transitory one, and it is 
quite possible that at a later stage interfascicular wood might have been formed. 
The peculiar form described in former memoirs under the name of Calamopitus,t 
may either come under this head or under B1. Here the interfascicular tissue does 
not appear to contain true tracheides, but the elements are very prosenchymatous, so 
that the character of the tissue is totally different from that of ordinary parenchy- 
matous rays. The prosenchymatous ray-cells of Calamopitus have no visible pits on 
their walls, and cannot well be classed as tracheides ; they differ from the tracheides 
in the wood of the same plant in shape and size, for the ray-cells are somewhat shorter 
and decidedly broader. In tangential sections, small parenchymatous secondary rays, 
sometimes only two cells in height, are seen between the prosenchymatous elements 
of the interfascicular tissue, like those between the tracheides of the fascicular wood.§ 
The whole structure shows a decided approach to that of Calamedendron Broner., of 
which we have examined some beautiful sections cut from a specimen found in the 
Permian of Chemnitz, and kindly presented to the collection by Count Soxms- 
Lavpacu. Calamodendron, however, is not known to occur in the English coal- 
measures, and we have not included it in the present paper. 
We think the genus Calamopitus should be retained. Besides the peculiar 
structure of its principal medullary rays it is characterized by the predominance of 
reticulated elements in its wvod, by the characteristic arch-like form of the commis- 
sural bundles at the node (as seen in tangential section), and by the very large and 
definite “infranodal canals.” Further information from additional specimens is 
however much needed. 
The sub-type A 2 is a very unimportant one, and has only been observed in two 
very small Calamitean stems, with wood not exceeding seventeen elements in radial 
* Bg, C.N. 13 and CN. 18. 
+ Hg., C.N. 33. 
t Wiuitamson, ‘Mem Lit.’ and ‘ Phil. Soc.,’ Manchester, ser. 3, vol. 4, 1869. ‘* Organization,” Part I., 
1871. 
§ Asin U.N. 54, 
MDCCUXCIV.—B. 5 U 
