HICK AND CASH: FOSSIL FLORA OF HALIFAX. 
373 
smaller spaces which appear to resemble air canals. On this point, 
however, our section is not clear, and we make this statement under 
cover of a reservation. Sometimes the cortex separates through 
this layer, leaving the inner cortical layer and the cambium behind, 
as is shown in other specimens in our possession. 
3. The outer Cortical layer (PI. 1, o.c.) consists of elements 
more or less rounded in transverse section, with thicker walls, and 
in many cases, black carbonaceous contents. They are not uniform 
in size, some being very much larger than the rest. Their exact 
histological nature can scarcely be said to be absolutely established, 
but there is some evidence that they are prosenchymatous cells or 
fibres. The best preserved and clearest parts of this portion of the 
section show few or no indications of the " hypodermal zone of 
specialised bundles " of apparently prosenchymatous tissue described 
by Prof. Williamson.* 
Other specimens in our possession, though agreeing with the 
above description in one or more particulars, present differences which 
ought to be noted. In some of these, there is little or no distinction 
between the inner and middle cortical layers ; and the large vessel- 
like elements of the former are less regularly arranged. The 
cambium, as might be expected, is often so compressed as to be 
almost obliterated ; while in other cases, it. as well as the delicate 
cells between the larger elements of the inner cortex, is a confused 
mass whose structure it is not easy to determine. 
A comparison of the above description with a transverse section 
of an Equisetum — E. arvense for example — will be found both inter- 
esting and suggestive. The pith and the vascular bundles of the 
fossil are evidently homologous with the parts, similarly named, of 
the recent plant. But the comparison gives support to the further 
view, that what we have termed the middle cortical layer of the 
fossil, with its presumed air canals, corresponds more or less closely 
with the inner cortex of the Equisetvm, in which air canals are also 
present. In that case, the inner cortical layer of the fossil must be 
regarded as part of the axial tissues. 
*" Organization of the Fossil Plants of the Coal Pleasures." Part XIL, 
p. 465. 
