252 HISTORY OF BRITISH FERNS, 



The section of the stem shows a small central cavity, an 

 exterior surface of rather prominent ridges, each channelled 

 so as to form two projecting angles, and a circle of moderate- 

 sized cavities occurring about the centre of the tissues. 



Insensibly merging into the form just described appears 

 to be another, that sometimes called U. arenarium, which, 

 in its extreme state, is smaller and more slender, its stems 

 always procumbent, and not having more than six furrows ; 

 in this form the teeth of the sheaths are said to be wedge- 

 shaped, but we do not detect any differences in respect to the 

 teeth between specimens having the erect and the prostrate 

 habit of growth. 



Another form, which is perhaps at least a permanent 

 variety, and may prove to be specifically distinct, is the 

 plant called K Wilsoni by Mr. Newman. With this we 

 are entirely unacquainted, except through books, in which 

 it is described as being stouter, taller three feet high and 

 smoother than the larger form of E. variegatum. The sec- 

 tion of its stem also differs materially; the central cavity 

 and the ring of cavities occurring in the cylinder of the stern 

 being much larger, and the latter differing in form from 

 those of E. variegatum. This variety grows in water, at 

 Mucruss, in the immediate vicinity of the Lakes of Kil- 



