ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 765 
belonged to the plant (fig. 30, Rt.). Other roots of the same kind occur in the 
preparations. 
We think it certain that this specimen does not belong to H. Grievit, or at least 
that it does not represent the ordinary form of stem in that species. We should 
have suggested that it might be a young specimen of H. tilieoides, were it not for 
the want of exact agreement in the details of the primary wood. Jt is possible that 
it may represent some peculiar form of stem, such as a rhizome, belonging to one or 
other of the known species. If it is desirable to give the specimen a provisional 
name, we may speak of it as H. cylindricum, but without desiring to imply that its 
claims to specific distinctness are likely to hold good permanently. 
IT]. Arginities or Lyginodendron ann Heterangium. 
So long as we are without information as to the reproductive organs of these 
genera, it is evident that any discussion of their affinities must be conducted with the 
greatest caution. Considering, however, the very thorough knowledge of their 
vegetative parts which we now possess, we may reasonably hope to throw consider- 
able light on the question, although we cannot yet solve it finally. Some encourage- 
ment in the attempt may be derived from the experience of paleeobotanists in other 
families. In the case of the Lepidodendree, for example, there can, we think, be no 
doubt that an unprejudiced consideration of their vegetative structure alone is 
sufficient to lead to a true estimate of their relationships, which is only confirmed by 
our knowledge of their fructifications. So also with the Calamariez ; as we showed 
in a former paper,* a minute examination of the anatomical characters, especially 
those of the primary tissues, affords by itself the strongest presumption of Equi- 
setaceous affinities, and so helps us to the right interpretation of the evidence from 
the fructifications. 
A really accurate knowledge of vegetative characters, especially of those derived 
from the internal structure, may,.we believe, be trusted to put us on to the right 
track in cases where the larger systematic groups are alone in question. 
The fact that in various respects both Lyginodendron and Heterangium strongly 
resemble Ferns has been noticed since the first discovery of these plants, and has been 
demonstrated in the preceding pages. As regards the former genus, we have now 
proved beyond doubt that the highly compound leaves were those of a Sphenopteris, 
and in Heterangiwm the general character of the foliage was evidently similar. The 
external form and even the venation of the leaf, however, would by themselves carry 
no decisive weight, though hundreds of fossil species have been referred to the Ferns 
on no better grounds. But beyond this, the internal structure of the leaf is now 
well known in Lyginodendron, and to a less degree in Heterangiwm, and proves to be 
in all respects that of a Fern, as is shown most clearly by the concentric structure of 
* Wi.uamson and Scort, “ Further Observations on the Organization,” &., Part I. 
