THE BRITISH HORSETAILS. 109 



ting in a cone-like head of spore-cases. The latter are taller, 

 and produce several whorls of long, crowded, slender 

 branches ; whilst a third kind produce both whorls of branches 

 and cones. In the production of these three kinds of stems it 

 serves to connect, through E. sylvaticum, that group in which 

 the fertile and barren stems are successive and altogether 

 unlike, with that in which the stems indifferently bear the 

 fructification. 



The fertile stems grow about six inches high, and are quite 

 branchless; they have numerous joints, the large loose funnel- 

 si] aped pale-coloured sheaths produced at these points, often 

 almost covering the stem. The teeth, which terminate the 

 sheaths, are awl-shaped, pale brown, with pale-coloured 

 membranous margins, and number from twelve to twenty, 

 equalling the ribs. The fructification forms a moderate-sized, 

 terminal, oval, cone-like head. 



The barren stems grow erect, eighteen inches or more in 

 height, and have on their surface about twenty sharp ridges, 

 with corresponding furrows, the ridges being coated with 

 prominent silicious warty particles, so that the stems are 

 very rough. The few lower joints are without branches, but 

 those in the upper part of the stem produce whorls of from 

 ten to sixteen branches, which are simple, and at first droop- 

 ing, but eventually become spreading. The sheaths of these 

 barren stems are much smaller than those of the fertile, less 

 funnel-shaped, and more closely set to the stem, and their 

 teeth are also fewer, shorter, and blunter. The branches are 

 slender, three or four-ribbed, and have loose sheaths, which 

 terminate in short, acute, membranous-edged teeth. 



The branched fertile stems have their sheaths smaller than 

 the simple fertile ones, but larger than the barren ones 

 Several of the uppermost joints produce whorls of branches, 

 and the stem is terminated by a cone of fructification. In 

 these cases, however, the number of branches is less than 

 that produced by the ordinary barren stems, and the cone is 

 smaller than those produced by the ordinary fertile stems. 



The section of the stem shows on the exterior a series of 

 sharp ridges with angular furrows ; the central cavity rather 

 exceeds a third of the whole diameter the cylinder of the 

 stem is then pierced by three circles of cavities one of 

 longish oblong openings opposite the furrows, one of minute 

 pores exterior to these and opposite the ridges, and another 

 of minute pores on their inner side also opposite the ridges. 



Probably this species is tolerably plentiful in moist shady 

 woods, which are the situations it affects ; but it has as yet 



