OF THE FOSSIL PLANTS OF THE COAL -MEASURES. 
299 
If I have correctly interpreted the facts just described, and I believe I have done 
so, the life-history of this plant throws an important light upon many of those described 
in the last, or second, of this series of memoirs. IIow far the numerous plants there 
referred to may prove to be different states of a few species is not easy to determine, 
because we do not obtain them in that condition of stratigraphical isolation which has 
afforded such an important help in the case of the Burntisland examples. In that memoir 
I pointed out how closely some of the Lepidodendroid forms resembled Coeda’s Diploxylon, 
and how the absorption of the cellular medulla of some of them would actually convert 
them into examples of the latter genus. It is necessary to remember that hitherto none 
of the authors who have written on Diploxylon have seen either its pith or its bark. 
The last description of Diploxylon published, so far as I am aware, with the exception of 
my own memoir, was that by Mr. Binney, who says of his specimen, “ although it shows 
the so-called medullary sheath in a very perfect state, there is nothing to indicate the 
former existence of a pith of cellular tissue”* * * § ; and he adds, “the part which remains 
undisturbed shows that the whole of the central axis was formerly composed of hexa- 
gonal vessels arranged without order “ this view is confirmed by another and more 
perfect specimen of Anabathra in my cabinet, and enables me to speak with positive 
certainty, and to show that these plants had a similar structure in the central axes to 
the specimens of Sigillaria vascularis described by me in my paper published in the 
Quarterly Journal of the Geological Society”f. 
Considering the imperfection of the materials at his disposal, no more discriminating 
account of these plants has been published than is contained in Professor King’s memoir 
entitled “ Contributions towards establishing the general characters of the genus Sigil- 
laria'%. In this memoir the author examines carefully the Anabathra of Witiiam, which 
is a true Diploxylon, and concludes that it is undoubtedly a Dicotyledonous plant ; but 
notwithstanding this mistake he correctly points out some of the features in which the 
genus approximates Lepidodendron, quoting Beongniaet’s suggestion as to the possibility 
of Diploxylon being the stem and Lepidodendron the branches of the same type of tree. 
With equal accuracy Professor King insists upon the truth, recently challenged by 
some of our younger botanists, that the vascular medullary cylinder and the exogenous 
ligneous zone are independent systems. 
In my previous memoir I also called attention to some of the observations of Beong- 
niaet and Coeda on Diploxylon , especially to an error into which the latter writer fell 
when he determined that no medullary rays existed in this genus. At the same time I 
explained the source of Coeda’s mistake, viz. his ignorance of the fact that the medul- 
lary rays of these plants sometimes consist of scalariform cells, but which he mistook for 
vessels §. Beongnlaet has made this supposed absence of medullary rays (which he only 
* “ On some Lower-Coal-seam Fossil Plants,” Philosophical Transactions, 1865, p. 584. 
f Loc. cit. p. 584. 
+ Edinburgh New Philosophical Journal, No. 71. 
§ It is an interesting circumstance that I have recently obtained from the Oldham Coal-measures a Stiyn.a- 
MDCCCLXXII. 2 S 
