48 
to which latter plant alone is referable Mr. Binney’s pre- 
viously published figures, M. Goeppert’s description and 
figures of which Mr. Binney approves, and mine which he 
rejects. 
Mr. Binney proceeds to say, “ . 'he size of these large vas- 
cular tubes or utricles in the medulla, exceeding anything, 
so far as his knowledge extended, hitherto observed in fossil 
plants, shows that it was easily decomposed, and thus 
accounts for the general absence of the medulla in Sigillaria 
and its roots.” At this reasoning I must altogether demur. 
Size has nothing whatever to do with the preservation of 
the tissues in fossil plants. Vascular structures strength- 
ened by transverse bars of lignine are equally well preserved 
whether they are large or small. The medulla of Stigmaria 
disappeared or became much disorganised because it con- 
sisted of an unusually delicate cellular tissue with extremely 
thin walls. This tendency to decay was more manifest 
towards the centre of the medulla than at its circumference. 
Specimens on the table exhibit this peripheral part of the 
cellular medulla in exquisite perfection, giving off its cha- 
racteristic cellular prolongations constituting the medullary 
rays, as described in my memoir. And yet this beautiful 
cellular tissue occupies the position which Mr. Binney says 
was occupied by “large vascular tubes or utricles.” The 
specimens referred to showing these conditions constitute 
unanswerable facts. 
Mr. Binney correctly notes the resemblance of the inner 
vascular cylinder in his specimen to a “ medullary sheath.” 
I have already said the same thing in several of my memoirs, 
and M. Brongniart said it before either of us. But this 
very homology, if correct, indicates the probability of Mr. 
Binney’s specimen being a fragment derived from the junc- 
tion of stem and root rather than a true root, since in 
living plants possessing a medullary sheath, that sheath, 
as every botanist knows, is never prolonged into the 
true roots, for the simple physiological reason that its origin 
