EQUISETUM. 2G7 



deep furrows, tlie number being variable, from six to eight. 

 The joints are invested with nearly cylindrical sheaths, 

 which are quite loose, being almost twice the diameter of 

 the stem in the upper parts of the plant ; the lower sheaths 

 are smaller and rather more funnel-shaped. The sheaths 

 terminate in as many acute wedge-shaped teeth as there 

 are ridges on the stem ; they are pale-coloured, tipped with 

 black or dark brown, and have membranous edges. 



The stems are usually, except at the base, furnished 

 with whorls of numerous simple branches, the number of 

 the branches generally corresponding with the furrows of 

 the stem. These are slender, four or five-ribbed, and 

 their sheaths set nearly close, and terminate in pale-brown 

 lance-shaped teeth, having a membranous border. 



In this species, when a section of the stem is examined, 

 it shows a series of prominent ridges on the outer face ; 

 just within these, and over against the furrows, occurs a 

 circle of moderate-sized cavities ; and alternating with 

 these, and near the inner margin, is a series of much 

 smaller circular cavities. The central cavity of the stem 

 is comparatively very small, not very much larger than the 

 series of openings near the outer surface. The resemblance 

 is considerable between its section and that of E. arvenss. 



