176 PROF. W. C. WILLIAMSON ON THE STRUCTURE 



I believe that the two specimens described are both from 

 the upper coal-measures. Fig. i was found in a sandstone 

 quarry near Oldham ; and though I am doubtful respecting 

 the precise locality whence fig. 2 was obtained^ I believe 

 that it came from near Peel. I have a similar specimen 

 from the Peel Delf-rock^ near Worsley, a sandstone be- 

 longing to the Upper Coal-measures. 



Since reading the preceding memoir, I have had the ad- 

 vantage of studying a very beautiful and important series 

 of sections of carboniferous plants, prepared and chiefly 

 collected by Mr. J. Butterworth, of High Crompton, near 

 Oldham. Amongst these are several instructive sections 

 of Calamites. This valuable contribution to microscopic 

 science requires me to modify one or two conclusions at 

 which I had previously arrived, since the specimens render 

 plain several points which were formerly obscure. Most 

 of them correspond very closely with Mr. Binney's ex- 

 amples in having the vascular tracts composed of scalari- 

 form vessels. But in one I can trace a decided transition 

 from the scalariform to the reticulated type, thus suggesting 

 the possibility of a link between Mr. Binney's specimens 

 and my own. Nor is this all ; in other specimens I find 

 the cellular tracts most variable in their structure. Some- 

 times the cells are elongated transversely, so that one long 

 cell extends horizontally across the cellular tract, reaching 

 from one vascular tract to another. In another example 

 the reverse is the case ; the cells are much elongated ver- 

 tically, but have rectangular extremities. In the same 

 tract these rectangular cells pass into the prosenchymatous 

 type, in which the ends of the cells diagonally overlap each 

 other; and yet in the same specimen are parts of cor- 

 responding tracts in which the cells are of the ordinary 



