156 PERNS OF GREAT BRITAIN. 



stems are alike, their branches greatly varying in length 

 in different circumstances. The cone of fructification is 

 slender, about an inch long, and standing on a foot- 

 stalk. The whorls of scales are, at an early period, 

 crowded into a black mass, but after a while are 

 quite separated, showing the white capsules attached to 

 the margin. In June, when these catkins are fully 

 ripened, they become of a brown colour, and, after dis- 

 charging the spores, wither away ; but the bright green 

 whorls of rigid branches remain green till late in the 

 autumn. 



There are some singular varieties of this plant, which, 

 however, appear to be dependent on soil and situa- 

 tion, and not to become permanent. One form has 

 been termed polystachion. Instead of the one cone 

 usually placed, in the ordinary form of the Horse-tail, 

 on the central stem, several of the branches of the two 

 upper whorls terminate in cones, which are usually 

 darker coloured than the commoner cone, more com- 

 pact in form, and appearing later in the season. 



Another, and rarer variety, called nudum, is very 

 much smaller than the ordinary plant, scarcely more 

 than three or four inches high, having the lower part of 

 the stem prostrate, and the branches only about the base 

 of its stem. It is apparently but a dwarfed condition of 

 the plant, caused by want of nutriment. The form 

 termed alpinum is very similar, and both are probably the 

 result of growth on a soil less favourable to luxuriance, 

 or of having been cropped by animals. 



6. K syhdticum (Wood Horse-tail). — Stem erect, 

 branches compound, bending downwards ; sheaths loose ; 



