4 
HICK : OUR KNOWLEDGE OF THE YORKSHIRE CALAMITY. 
According to Grand 'Eury* there were other species of 
Calamitw, which, instead of being tufted like the above, grew singly, 
their narrowed and fusiform extremities passing vertically down- 
wards, and giving off* from the nodes close whorls of long, simple, 
descending roots. 
Now it is a possible, if not a probable hypothesis, that these 
various kinds of shoots and branches should have a correspondingly 
variable internal structure, but we have no positive evidence by 
which this, or indeed any other hypothesis, can be tested. One 
would like to know too whether any of these, and if so which, were 
capable of unlimited growth, for although some of them were capable 
of secondary growth in thickness, it does not follow necessarily that 
they were perennial. Where branching occurred the branches were 
in some forms solitary and in others whorled, but we have nothing to 
show in what way these various habits were correlated with internal 
organisation. 
As regards the structure of the aerial stems we are in a some- 
what better position, as this is now tolerably well-known, at least in 
a general way. In saying this it must be remembered that I am 
speaking only of Yorkshire specimens with structure, all of which 
belong to the type now known as Arthropitys. Still it may be 
mentioned that the Lancashire specimens belong to the same type, so 
that as far as present knowledge goes, this is the only type found in 
the Yorkshire and Lancashire Coal Measures, with the structure 
preserved. 
In a paper read by Mr. Cash and myself before this Society in 
1883,| an account was given of the anatomy of the stem as it was 
then known, and attention was specially called to the light thrown 
upon the cortex by a specimen discovered by Mr. Spencer. I believe 
that specimen still remains the most perfect one hitherto described 
and published, but we are now in possession of others which afford 
additional information, not only upon the anatomy of the stem as a 
whole, but also on its development from the condition of a twig to 
that of a stout shoot. Unfortunately, a description of these cannot 
* Flore Carbonifere du dept. de la Loire et du centre de la France, 
t Proc. Yorksh. Geol. & Polyt. Soc, N.S., vol. iii. 
