OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
215 
bark. In the memoir just referred to*, Mr. Binney recognizes the medullary rays, but 
again adopts Goeppert’s explanation of the origin of the vascular rootlet-bundles, and 
gives a figure of a specimen which he supposed afforded confirmation of this explanation, 
having ten or twelve large vessels, as he believed, in the pith, “ each of about one tenth 
of an inch in diameter.” The largest vessels which I have seen in the woody stems of 
Stigmaria do not exceed ‘005 in diameter, whilst those going to the rootlets are gene- 
rally much smaller. I have elsewhere called attention to the way in which the rootlets 
of Stigmaria have penetrated every thing within their reach that was penetrable ; and I 
have no doubt that in both Professor Goeppert’s and Mr. Binney’s specimens, these 
supposed medullary vessels were really Stigmarian rootlets that had found their way 
into the interior of the cavity left by the decay of the medulla, and been mistaken for a 
part of the plant into which they had intruded themselves f. Mr. Binney, in 1857, 
discovered the structure of the rootlet of Stigmaria , and also gave the first insight into 
the nature of the outer bark. In some specimens supplied to him by Mr. Bussell, of 
Airdrie, he found remains of an outer radiating cylinder, at a considerable distance from 
the inner one, and upon which the rootlets were planted. This outer cylinder Mr. 
Binxey described as consisting of “ wedge-shaped masses of tubes or elongated utricles” J. 
With this discovery progress virtually ceased. The subsequent history has mainly 
been one of retrogression. Notwithstanding the clear statements of Hooker, and the 
equally accurate figures of Broxgxiart, it has become the fashion to deny the presence 
of medullary rays in Stigmaria. This has been done on several occasions by my friend 
and fellow labourer in this field of research, Mr. Carrutiiers ; but I think I shall be 
able to demonstrate that, for once, his usually accurate powers of observations have 
failed him, owing partly to his not having seen the best specimens, and partly to his 
general objection to the recognition of medullary rays in the stems of these Palseozoic 
Cryptogams. Mr. Carrutliers states that he has met with one specimen in which the 
central axis exhibits elongated scalariform cells. Not one of my numerous specimens 
contains a trace of any such structure. I speak with hesitation as to the cells of the 
central part of the medulla, because even when present these cells are almost always 
disintegrated ; but so far as the more peripheral ones of the pith of the true Stigmaria 
were concerned, I have the clearest proofs that they never were barred. 
I am convinced that one cause of the discrepancies that exist amongst writers on this 
subject has been the want of an exact definition of a Stigmaria, several very distinct 
roots having been included in the term. But the plants described by Broxgxiart, 
* Some observations on Stigmaria (Joe. cit. pi. iv. fig. 2). 
t I bave before me at the present moment a section of a large Lejoidodendron of which' the woody axis and 
its medullary centre have disappeared, the thick cortical layer alone remaining. A large Stigmarian root has 
found its way into the cavity and filled it up, giving off its peculiar rootlets within the Lepidodendroid cylinder. 
Such a specimen would inevitably mislead even a botanist, whose eye was not familiar with the appearances of 
the two plants. 
^ Philosophical Transactions, 1865, p. 593. and woodcut 4. 
2 f 2 
JC -J 
