96 



On the Fossil Plants of the Coal-measures. [Jan. 11, 



an enormously thick bark. The structure just descibed is that of a true 

 example of the genus Diploxylon of Corda. But I have got abundance 

 of specimens with leaves on the exterior of the bark, demonstrating that 

 the plant is a true Lomatophloios, thus indicating the correctness of my 

 supposition, advanced in my last memoir, that sooner or later the genus 

 Diploxylon would have to be abandoned. 



As if to place beyond doubt the accuracy of these interpretations, I have 

 now got magnificent specimens, apparently representative of a cambium layer, 

 in which the half-grown vessels and the imperfectly formed medullary rays 

 are exquisitely clear. In addition to these discoveries I have obtained a 

 Lepidostrohus, which I have no doubt is the fruit of the above plant. It is 

 provided with both microspores and macrospores, the exteriors of the latter 

 being curiously furnished with numerous caudate prolongations, causing 

 them to resemble some of the fossil Xanthidia of the chalk. 



I have further obtained, both from Lancashire and Burntisland, beau- 

 tiful stems of another type, and which I have no doubt belong to Astero- 

 phyllites. These began to grow, as before, with a central vascular bundle 

 surrounded by a cylinder of parenchyma, but the transverse section of the 

 bundle soon became triquetrous instead of circular. This, it may be remem- 

 bered, is the characteristic of the corresponding bundle of the strobilus which 

 I have just described in the ' Transactions of the Literary and Philosophical 

 Society of Manchester,' under the name Volkmannia Dawsoni, and which 

 I referred to Asterophyllites. This central triangular axis does not ex- 

 pand or become converted into a hollow cylinder ; but vessels are at once 

 added to each of its three sides, exogenously, and in radiating series, until 

 it becomes converted into a cylindrical woody axis. I have specimens show- 

 ing the nodes and internodes, leaving little, if any, room to doubt the close 

 affinity between the plant in question and the verticillate-leaved Astero- 

 phyllites. 



The details of these discoveries, along with those respecting a most re- 

 markable series of Lycopodiaceous plants, to which I have given the name 

 of Dictyoxylon, but which name will have to be abandoned for the late 

 Mr. GourhVs name of Lyginodendron, will be laid before the Royal Society 

 with as little delay as possible. I may observe that the plants last re- 

 ferred to have developed, so far as type is concerned, in a way very similar 

 to that of the Lomatophloios, allowance being made for generic and specific 

 peculiarities. 



I am, my dear Sir, 



Very sincerely yours, 



W. C. Williamson. 

 I ought not to close this letter without acknowledging the indefatigable 

 energy of G. Grieve, Esq., of Burntisland, who has supplied me with a 

 constant stream of specimens, upon which I have been able to operate, thus 

 rendering an admirable service to the cause of palseophytology. 



