THE BKITISH HORSETAILS. 113 



circle of angular cavities close to the inner margin of the 

 tube. The central cavity measures about half the dia- 

 meter. 



This species grows naturally in moist shady woods ; and 

 though local, owing apparently to the conditions necessary 

 to its growth,_ namely, shade and moisture combined in a 

 peculiar way, it is, nevertheless, a widely distributed plant, 

 And can hardly be considered as uncommon throughout the 

 United Kingdom. Its fertile stems are in perfection about 

 the middle of April, and its barren stems in June. 



THE WATER HORSETAIL. 



This, the Equisetum limosum of botanists, is sometimes 

 called the Smooth Naked Horsetail. It is a common species 

 and generally distributed, occurring principally in pools, 

 ditches, and marshy places, though occasionally in running 

 streams. It is rather tall-growing, the stems rising from two 

 to three feet or more in height ; these, though finely ribbed, 

 are smooth to the touch, the furrows being very shallow; 

 their smoothness no doubt arising from the coating of sili- 

 cious particles being much finer and less prominent than in 

 others which are more harsh to the touch. Sometimes the 

 stems are quite unbranched, sometimes furnished with irre- 

 gular whorls of branches along all their central portion ; and 

 between these two extremes there occurs every conceivable 

 degree of branching, from the single shoot produced here and 

 there, through every gradation of imperfect whorls up to 

 whorls of short branches almost complete. The branches, 

 which are simple, nearly erect, and never acquire much 

 length, are from four-angled to eight-angled, and are smooth 

 like the stem. There is no material difference between the 

 barren and fertile stems, except the presence of the fructifi- 

 cation in the one case and not in the other. 



The surface of the stem is marked with from sixteen to 

 twenty very slight ridges, and the sheaths, which are short, 

 rather closely fitted to the stem, and of the same colour in 

 the lower part, terminate in an equal number of dark- 

 coloured awl-shaped teeth, which sometimes have a pale 

 membranous margin. 



Owing to the shallowness of the ridges and furrows, the 

 section of the stem shows a nearly smooth exterior outline, 

 and the cylinder of the stem is furnished only with a row 

 of minute cavities near the inner margin ; this cylinder is 

 very thin compared with the diameter of the stem, the cen- 

 tral cavity being unusually large. 



H 



