ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 867 
of these fossils in the English Coal-Measures is that of the so-called Arthropitys, 
Gépr. As this genus was only separated from Calamites on account of its secondary 
zone of wood, which we now know to have been common to the whole group, we shall 
retain the older generic name. The question, so keenly discussed since the time of 
Bronenrart, as to the Cryptogamic or Phanerogamic nature of these remains, seems 
now to be definitely decided in favour of the former alternative.t As regards the 
vegetative organs, the presumption, derived from the occurrence and character of the 
secondary formations, seemed at first entirely in favour of Phanerogamic affinities, and 
we cannot wonder at the view so long held by Bronentart and many botanists of his 
school. Only a consideration of the whole body of evidence, both from recent and 
fossil plants, has decisively turned the scale the other way. 
Among the Cryptogams the affinities of Oulamites have always been sought in the 
neighbourhood of the Equisetaceze. In considering the vegetative organs, then, the 
most interesting question is whether the primary structure shows a sufficiently close 
agreement with that of Hquisetum to establish any presumption of relationship. 
The most obvious resemblances, which attracted the attention of the earlier paleo- 
botanists, have turned out to be fallacious. Thus we now know that the supposed 
Equisetum-like ribbed stem is no ribbed stem at all, but merely a cast of the pith- 
cavity. The external surface of the larger specimens could not possibly have shown 
tibs like those of Equisetum, for in the latter genus these ribs represent the course 
of the vascular bundles, and these are overlaid in the older Calamites by an immense 
zone of secondary wood and cortex.{ 
The points of vegetative structure on which stress may fairly be laid, for purposes 
of comparison with Hguisetum, are the following :— 
1. The arrangement, and relative position of leaves, branches, and adventitious 
roots. 
2. The course of the vascular bundles. 
3. Their orientation, and the order of development of their elements. 
4. The details of histological structure. 
The points under the first category are of manifest morphological importance; the 
others are each, by themselves, of secondary value, and only a strong resemblance in 
the sum of such characters could weigh for much in estimating affinities. 
* Cf. Granp’Hory, “ Calamariées—Arthropitus et Calamodendron,” ‘Comptes Rendus,’ 1889, vol. 108, 
p. 1086; also ‘Flore Carbonifére du Gard,’ 1890. 
+ We believe that M. Renavit is now the only author who still attributes Phanerogamic fructifi- 
cations to some of the Calamariew. See his “ Etude sur le Terrain Houillier de Commentry,” livre 2, 
‘Flore Fossile,’ Part IT. 
{ The shorter-lived branches no doubt had a comparatively thin secondary zone, and these, in the 
fossil state, may appear to show superficial markings. It has already been shown that these markings 
are simply due to the ribs of the medullary cast, which have become impressed on the thin carbonaceous 
layer to which the external tissues are reduced (see WiLtLIamson, “‘ Organization,” Part I., ‘ Phil. Trans.,’ 
1871, p. 495). 
