404 HICK AND CASH : FLORA OF LOWER COAL MEASURES. 
cortex, and in others anastomose freely. Comparing our fossil 
with these plants, we find that it has many points of resemblance 
to the stem of Myriophyllum. In both there is an axial string, com- 
posed of fibro- vascular bundles, and a comparatively thick cortex, in 
which are longitudinal cavities, separated by thin plates of paren- 
chyma. In histological structure, the cortex of both the recent 
and the fossil form is almost identical. The axial string, however, 
is not quite the same in the two cases. In the fossil it exhibits a 
distinction into pith and fibro- vascular bundles, which, as we 
have already said, are arranged somewhat as in dicotyledons. But 
in Myriophyllum the axial string is composed of a thin-walled 
cambiform tissue, and is enclosed in a well denned fibro-vascular 
bundle sheath. There is, however, no distinct separation of pith 
and bundles as occurs in the fossil specimen, nor is there anything 
comparable to a cambium zone. This is no doubt a most important 
difference, and one to which we are disposed to attach consider- 
able weight. The form of the bundles, and presence of the cam- 
bium, seem to indicate that the fossil plant was capable of growing 
in diameter in the same manner as an ordinary dicotyledon, but 
this can hardly be said of the modern Myriophyllum. 
For this addition to our Fossil Flora, we have once more to 
record our thanks to our indefatigable friend, Mr. James Binns, 
of Warley, near Halifax, who has already furnished us with several 
new forms. 
In honour of Professor W. C. Williamson, F.R.S.. who has 
done so much by his labours and prolonged investigations to 
elucidate the organisation of Carboniferous plants, we propose to 
designate our specimen, — " Myriophylloides Williamsoni" 
Table of Dimensions. 
Diameter of pith alone -042 inch. 
Breadth of vascular zone ... *007 ,, 
Diameter of axial string ... '056 
