404 Royal Society. 



stem, the chief bulk of which consists of 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 Lomutophloios, thus indicating the correctness of my suppo- 

 sition, 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, 

 beautiful stems of another type, and which I have no doubt belong 

 to Asterophyllites. 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 remembered, 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 of Volkmannia Dawsoni, and which I 

 referred to Asterophyllites. This central triangular axis does not 

 expand or become converted into a hollow cylinder ; but vessels are 

 at once added to each of its three sides, exogenously, and in radia- 

 ting series, until it becomes converted into a cylindrical woody axis. 

 I have specimens showing the nodes and internodes, leaving little, if 

 any, room to doubt the close affinity between the plant in question 

 and the verticillate-leaved Asterophyllites. 



The details of these discoveries, along with those respecting a 

 most remarkable series of Lycopodiaceous plants, to which I have 

 given the name of Dictyoxylon (but this will have to be aban- 

 doned for the late Mr. Gourlie's name of Lyginodendron), will be 

 laid before the Royal Society with as little delay as possible. I 

 may observe that the plants last referred to have developed, so far 

 as type is concerned, in a way very similar to that of the Lomato- 

 phloios, 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 inde- 

 fatigable 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. 



