The Carboniferous Arborescent Lepidodendra. 45 



452, also requires a few words of explanation. As already- 

 mentioned, at Laggan Bay the bases of thirteen large stems 

 stood erect and closely aggregated. Further investigation 

 shewed that twelve of these were merely cylinders of outer 

 cortex, all their more internal tissues having disappeared 

 and been replaced by volcanic ash, with which the trees 

 had been destroyed and buried. The decay of the softer 

 portions of the bark had loosened all the harder vascular 

 structures compassing their several steles, and allowed them 

 to float out when the area became submerged. But the 

 exceptional stem had met with different treatment. In the 

 first instance it also had lost all its vegetable contents, which 

 had evidently floated out upon the neighbouring waters. 

 Directed by some fortunate current, a quantity of the 

 floating debris had been washed back into and filled the 

 vacant cavity of the thirteenth stem. Further examination 

 of this debris shewed that it consisted of fragments of bark 

 and of Stigmarice rootlets, including a fragment of a vascular 

 axis of a Stigmaria ; but what was still more important, 

 we found in it the entire and fully developed steles of no 

 less than five of the remaining trees which had been tumbled 

 into this single one. A perfect section of this entire stem, 

 with all its contents, is now in my collection, and the basal 

 portion of the same stem, equally rich in similarly precious 

 remains, is in the Museum of the Owens College, Manchester, 

 to which I presented it. 



My cabinets contain several fine sections of the steles 

 thus obtained, most of which had attained to about the 

 same measure of growth and maturity. One of the finest 

 of these, of which my C.N. 452 is a section, is represented 

 by the Figs 6 and 6a of my Memoir X. The diameter of 

 its Primary Xylem cylinder is 22 mm., enclosing a large 

 medulla, and containing about 6,900 tracheids. Its cylinder 

 of Secondary Xylem has a diameter of 69 mm. 



In my sections of this type I have examples alike of 



