404 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
of their curious organization will be made the subject of a future memoir. It follows 
from the previous determinations that the bark of D. Grievii is essentially a mass of 
coalesced petioles. The final question to be asked is difficult to answer. What are the 
mutual relations and botanical affinities of the two plants which I have described 1 That 
they possess many points of close mutual resemblance is obvious from the preceding 
descriptions, especially in their reticulated vessels, in the general aspects and arrange- 
ment of their cortical vascular bundles, in their root-like appendages, and especially in 
the structure of the parenchymatous portions of the bark. On the other hand, they 
exhibit some equally obvious differences, especially in the composition of the vasculo- 
cellular medullary axis and in the very different dimensions attained by their exogenous 
ligneous zones. There is now no room whatever for doubting that the Lyginodendron of 
Mr. Gourlie is a sandstone impression of the exterior of the bark of a plant like 
Dictyoxylon Oldhamium, if it does not, as I think exceedingly possible, represent the 
arborescent condition of the same species ; but since the latter point is not clearly esta- 
blished, it will be more prudent to retain, for the present, Mr. Binney’s specific name. 
On the other hand, my generic name of Dictyoxylon must clearly be abandoned for that 
of Mr. Gourlie, so that the plant in question may henceforth be recognized as Lygino- 
dendron Oldhamium. If at any future period specimens having the internal organiza- 
tion of our Oldham plant should be found at the Ayrshire district, whence the Eev. 
David Landsborough obtained his casts, it may then become necessary to adopt 
Mr. Gourlie’s name of Lyginodendron Landsburghii in its totality. 
In plate xvii. of his ‘ Flora der Vorwelt,’ Corda published sections of a fragment of a 
plant which he obtained from the Bohemian Coal-measures, and to which he gave the 
name of Heterangium paradoxum. This specimen only exhibited a small portion of the 
vasculo-medullary axis ; but, so far as it goes, the structure which he figures and describes 
appears identical with the corresponding portion of my Dictyoxylon Grievii. Since no trace 
of the bark exists in his specimen, we cannot identify the species of the German botanist 
with the Burntisland plant. But I think there can be no doubt that the two objects are 
generically identical. This circumstance in some degree affects the question whether the 
two plants which I have just described should be united in one genus or separated into 
two. On this point I entertain serious doubts ; but if the latter plan be adopted, then 
my Dictyoxylon Grievii must be recognized as Heterangium Grievii. By acting thus we 
not only create no new genus, but, by the extinction of my new term Dictyoxylon , 
actually reduce the existing number ; hence, for the present, it may be desirable to adopt 
this plan. If further research should bring the two plants yet closer together, then 
Mr. Gourlie’s, being the oldest of all these generic terms, must be adopted for both. 
The accident of Corda’s introduction of a fragment of Lyginodendron amongst his figures, 
under the name of Sagenaria fusiformis, is so obviously a blunder, that this still 
more ancient generic term may be excluded from our consideration. 
W e must not forget that all these names are merely provisional ones. These and 
numerous other stems that are the subject of research doubtless belong, in most 
