EQUISETACE^E. 159 



which have not only a spike on the main stem, but also minute ones 

 on the branches, which are much elongated. 



The barren fronds of E. palustre are much like those of E. arvense, 

 but may be readily distinguished by the teeth of the stem-sheaths 

 being darker, and with a broader white margin ; by the minute 

 sheaths from which the branches spring being pitchy-brown or black 

 and shining; by the branches being hollow and most commonly 

 5-angled, and with the faces between the angles not excavated into 

 deep grooves ; by the teeth of the sheaths of the branches being much 

 shorter and sulcate ; and above all, by the first internode of the 

 branches being extremely short, rarely reaching even to the base of 

 the teeth of the stem-sheath, while in E. arvense it almost always 

 exceeds the apex of the teeth of the stem-sheath. 



Marsh Horsetail. 



SPECIES VI.— EQUI SET UM LIMOSUM. Smith. 



Plate 1893. 



E. fluviatile (Linn.), Newm. Brit. Ferns, ed. ii. p. 51. Hartm. Handb. Skand. Fl. ed. xi. 

 p. 548. Non Sm. 



Stems all similar, perishing in autumn. Sterile stem stout, rarely 

 rather slender, not furrowed when fresh, but with 10 to 25 faint 

 striae (which are more conspicuous in the dried plant), smooth, green. 

 Sheaths shortly cylindrical or funnel-shaped-cylindrical, green, often 

 pitchy-black towards the apex ; teeth 10 to 25, mostly free, but 

 sometimes united in pairs or threes, narrowly triangular or triangular- 

 subulate, acute, usually pitchy-black or at least tipped with that 

 colour, with very narrow pale brown scarious margins. Branches 

 usually in whorls, but sometimes only 1 or 2 from a node, and often 

 wholly absent, generally 4-angular but sometimes 5- to 6-angled, with 

 the ridges separated by very shallow furrows, hollow, unbranched, 

 their lowest internode shorter than the teeth of the sheath-stem 

 below which it is produced; sheath enclosing the base of the first 

 internode of the branch pitchy-brown or olive, dim with deltoid-ovate 

 subacute teeth, without whitish margins ; sheath at the apex of the 

 first internode terminated by triangular-acute teeth, and those of the 

 succeeding internodes with subulate very acute teeth. Fertile stem 

 differing from the sterile one only in being terminated by a spike 

 which is oval-ovoid or ovoid-oblong, obtuse, pitchy-black or pitchy- 

 brown. 



