THE SCOURING-RUSHES. 



35 



height of two feet or more, with a diameter of a quarter 

 of an inch. They contain from ten to thirty grooves, 

 the ridges somewhat rounded and usually rough with 

 many cross-bands of silex. The sheaths are twice as 

 long as they are wide, and are tipped with triangular, 

 long-pointed teeth, most of which are torn off by the 

 developing stems, the rest falling at maturity. The 

 teeth are dark brown or black with a pale margin, and 

 the bases, which remain attached to the sheaths, are 

 slightly grooved in the centre. Each leaf has a low 

 ridge extending lengthwise, and the upper margin, where 

 it is separated from the others, is slightly raised. In 

 cross-section more than four fifths of the stem is hollow, 

 and both the carinal and vallecular canals are very small, 

 or, occasionally, wanting. 



Much remains to be observed regarding the 

 development and duration of the stems of this 

 species. Apparently the erect fruiting stems 

 do not branch, at least not until after fruiting, 

 but the sterile stems produce regular whorls 

 of branches as they develop. There is also 

 a form of the sterile stem, most noticeable in 

 winter, which spreads flat on the ground and 

 sends out a multitude of short, very slender 

 branches from the base, forming dense mats. 

 In this form the stems are about ten-angled, 

 and the teeth are silvery white and persistent. 

 It does not seem to be known whether the 

 fertile and sterile stems last through the win- Eguiseticu 



. . r 1 1 r 1 1 Fiinstoni. 



ter, but, reasonmg from the analogy of related 

 species, it may be assumed that they do. 



The fruiting-catkins are among the largest produced by 

 this group of plants, being about three quarters of an 



