162 FERNS OF GREAT BRITAIN. 



toothed ribs, a character which is very useful in deter- 

 mining the species, 



The fertile stems of this species are much shorter than 

 the barren ones, rarely exceeding a foot in height. They 

 are succulent, reddish-white, smooth, and unbranched, 

 with large, loose, funnelrshaped sheaths, the lower ones 

 smaller than the upper. These sheaths, which are pale 

 green at the lower, and dark brown at the higher part, are 

 distinctly marked with lines, and have from thirty to forty 

 long slender teeth. The catkins are two or three inches 

 long, and have an immense number of scales arranged 

 in whorls around them, the lower scales forming distinct 

 rings. 



This is not an uncommon, though a somewhat local 

 plant ; and notwithstanding its name of Water Horse- 

 tail, grows quite as often, or more so, on sandy or clayey 

 moist soils, as on the borders of rivers or ponds, nor is it 

 frequently, if ever, to be seen growing in the water. Its 

 underground stem creeps far in the moist earth, where its 

 black wiry roots increase rapidly, and are Yery abundant. 



When this Horsetail grows in large masses, as it 

 sometimes does in the neighbourhood of London, a third 

 kind of stem is occasionally to be found in August, 

 smaller and shorter than the ordinary stem, its sheaths 

 less spreading, and its cone smaller. This is a dwarfed 

 form of the plant, owing to the spot on which it occurs 

 being not sufficiently moist for its luxuriant growth. 



9. ^, variegdiitm (Variegated Rough Horsetail). — 

 Stems traihng or erect \ sheaths black at the top ; teeth 

 few, white, not falling off. This is one of the plants of 



