EQUISETACE.E 113 



in a warm situation, in which condition they attained a large amount of 

 independence, and propagated freely by budding. 



The number of known species of Equisetum, commonly known as 

 ' horsetails,' does not exceed 20 or 25 ; they are most numerous in the 

 temperate regions, decreasing in number both towards the pole and the 

 equator, and are very rare in the Southern Hemisphere. The stem is 

 always very slender, and seldom exceeds two or three feet in height, 

 though E. giganteum (L.) reache/ 20 to 40 feet in the tropics, with a 

 climbing habit. Most of the species prefer loose sandy or gravelly soil 

 in damp situations ; several grow in marshes or standing water. The 

 erect stems are mostly annual, but in a few species they endure for 

 several years ; while the rhizome is always perennial, and frequently 

 attains great size both in depth and in lateral extension. The species 

 are all remarkably similar in habit, differing chiefly in the presence or 

 absence of special fertile stems, the position of the stomates, and the 

 degree of branching ; but the classification of the species into two dis- 

 tinct groups of ' homophyadic ' and 'heterophyadic ' is not a natural one. 

 Each species is also characterised by a special arrangement of the 

 1 vascular ' bundles, and of the air-cavities as seen in a transverse section 

 of the stem. In external form, but not in internal structure, they call 

 to mind Ephedra among Gymnosperms, and Casuarina among Angio- 

 sperms. The large amount of silex deposited in the epiderm renders 

 several species, especially E. hyemale, useful for scouring purposes, and 

 they are popularly known under the name of ' Dutch rushes.' 



LITERATURE. 



Cramer in Nageli u. Cramer's Pflanzenphys. Unters., vol. iii., 1855. 



Sanio (Epiderm and Stomates) Linnsea, 1857-8, p. 385. 



Duval-Jouve Hist. Nat. des Equisetum, 1864. 



Rees (Apex of stem) Pringsheim's Jahrb. wiss. Bot., 1867, p. 209. 



Milde Monographia Equisetorum, 1867. 



Pfitzer (Bundle-sheath) Pringsheim's Jahrb. wiss. Bot., 1867, p. 297. 



Famintzin (Buds) Bull. Acad. Sc. St. Petersburg, vol. ix., 1876. 



Campbell (Pro thallium) Amer. Natural., 1883, p. 10. 



Leclerc du Sablon (Sporange) Bull.. Soc. Bot. France, 1884, p. 292; and Ann. 



Sc. Nat. (Bot.), vol. ii., 1885, p. 5. 



Goebel (Fertile shoots) Ber. Deutsch. Bot. Gesell., 1886, p. 184. 

 Buchtien (Oophyte) Uhlworm and Haenlein's Biblioth. Bot., Heft 8, 1887. 



