286 
HICK: calamostachys binneyaha. 
thin walls, a circumstance which readily accounts for the frequency 
with which it disappears in the process of fossilisation. On the out- 
side of the inner parenchyma we have the hypoderma, h, which is 
thickwalled, and whose elements are somewhat uniform in *ize, and 
in some cases have apparently possessed copious contents. In dif- 
ferent specimens and probably in different parts of the same specimen 
the character of the hypoderma varies a little, especially in the wall 
thickening and the density of the cell contents. As has been shown 
by previous authors, the hypodermal elements are elongated longitu- 
dinally and are prosenchyinatous. 
In none of the sections is there shown a distinct epidermis, but 
in one or two instances hairs are met with between the sporangia 
which seem to have been connected with an epidermal layer. 
The Nodal Disks and Bracts. 
According to Carruthers* the disks are composed of large 
roundish cells and the bracts of smaller and more elongated elements, 
while a slender vascular bundle enters each bract from the axis. 
Williamsouf describes the disk as consisting of " two kinds of coarse 
thick-walled cellular tissue,' 5 broad lines of cells elongated in the 
plane of the disk leading from the axis to the base of each bract, 
while the intermediate triangular areas are occupied by a coarse 
parenchyma. In a later MemoirJ he tells us that the prosenchy- 
inatous cells are found only on the upper surface of the disk, and 
that " the bundle of small spiral vessels " runs " along the center 
of the lines " they form. To these statements we are in a position 
to make one or two important additions. The disks of one of the 
best preserved specimens have a thickness of 0'559 mm., and the 
vascular strands run about midway between the upper and lower 
surfaces. But near the periphery a layer of cells is differentiated 
beneath the vascular strands which neither Carruthers, Williamson, 
nor any other writer appears to have noticed. It consists of large 
elements of variable size, whose walls are thin and whose luinina are 
occupied by dense masses of some black substance which is probably 
carbonaceous. 
*Loc. cit., p. 350. t Op. cit., \\. v., 1871, p. Co. 
X Op. cit., Ft. x., 1810, p. 503. 
