168 ENGLISH BOTANY. 



the back, but slightly grooved, and present two sharp angles towards 

 the furrows, and the rough points with which they are furnished 

 are arranged in two distinct lines. The sculpture of the sheaths and 

 teeth is different, the central furrow running into each tooth is deeper, 

 and the lateral furrows are wider and shallower than in E. Moorei. 

 The points of the teeth are firmer, not being wholly scarious, but 

 having a furrowed rib of firm tissue running along them ; this rib 

 is of a pitchy-black colour, and is bordered with pale or whitish 

 scarious margins. The teeth are much more persistent ; the sheaths 

 become sooner black and remain much longer so, not assuming a 

 whitish tinge until the winter. The stems are completely evergreen. 

 I have not found it injured by frost since 1876, when I received 

 living specimens from Mr. S. A. Stewart, of Belfast, which have grown 

 in the open ground up to 1881. 



Mackays Horsetail. 



SPECIES IX.— E QUISETUM VARIEGATUM. Schlekh. 



Plates 1897 and 1898. 



Babenh. Crypt. Vase. Europ. Exsicc. Nos. 73 and 98. 



Stems all similar, completely evergreen, usually several together 

 from each branch of the rootstock, slender or rather slender, rarely 

 stout, with a central hollow of one-fifth to one-third of its diameter, 

 with 4 to 12 shallow furrows separated by subacute-angled ridges, 

 which are rough with small prominent tubercles arranged in two 

 lines on each ridge and furrowed on the back, dull dark green. 

 Sheaths shortly (rarely longly) cylindrical-turbinate, yellowish-green, 

 at first concolorous, then with a black band at the apex ultimately 

 extending downwards until nearly the whole sheath becomes black, 

 but usually without a black band at the base, and rarely wholly black, 

 each of the portions of the sheath which corresponds with one of the 

 teeth with a rather broad deep furrow in the centre, and another 

 broad shallow rather indistinct furrow on each side between the 

 central furrow and the great furrow which extends between the teeth 

 from the apex to the base of the sheath ; teeth 4 to 12, triangular- 

 lanceolate or triangular-ovate, abruptly or rather abruptly acu- 

 minated into setaceous straight rough firm mostly caducous points, 

 pitchy-black with broad white scarious margins, furrowed on the 

 back, persistent, though generally their points either fall or get 

 broken off, occasionally becoming nearly wholly white when old. 

 Branches rarely produced unless the main stem has been injured 



