EQUISETUM. 223 



of this race of plants. They are divided at intervals into 

 joints of variable length, the number of joints being also 

 variable, from six on stems of about four inches in length, 

 to eight on those which measure eight inches, though some- 

 times specimens of equal length have but five or six joints. 

 From this cause they are much more distant on some stems 

 than on others ; a space measuring three-quarters of an 

 inch being sometimes interposed between the top of one 

 sheath and the base of the next above it. On the other 

 hand, they are sometimes so close as nearly to touch ; but 

 we have seen no instance in which the base of a sheath is 

 covered by the sheath below it, except at the very lowest 

 part of the stem, where they become much reduced in size, 

 and are sometimes crowded. It is usual for each succeeding 

 joint upwards to be somewhat more distant than the one 

 beneath it. The sheaths are large and loose, widening up- 

 wards ; they are pale-coloured, somewhat yellowish at the 

 base, and are divided above into about ten dark brown teeth, 

 which often adhere together in twos and threes. The teeth 

 are very narrowly lance-shaped and sharp-pointed, and are 

 the terminations of the ribs, about ten in number, by which 

 the sheaths are marked. 



These stems are terminated by cone-like heads, bearing 



