THE PERN ALLIES. 3^ 



LITERATURE. 



Hooker (W. J.) and Baker (J. G.)- Synopsis Filicum, pp. 

 444-448. 



MiLDE (J.). Botrychiorum Monographia. In Verhandl. der 

 k.k. zool. bot. Gesellsckaft.yiviu, 507-516 (1868); xix, 55-igo; 

 Tafel VII, VIII (1869); xx, 999-1002 (1870). 



Davenport (George E.), Notes on Botrychium simplex. 

 4to, paper, with plates (1877). 



Vernation in Botrychia. In Torrey Bulletin, '•^l, \()2r 



199, plate (1878) ; vii, 115, 116 (1880) ; vill, 100, loi (1881). Cf. 

 also XII, 22, 23. 



Campbell (Douglas H.). The Development of the Root in 

 Botrychium iernatum. In Botanical Gazette, xi, 49-53, with 

 plate (March, 1886). 



A Method of Spore Germination. In Botanical Ga- 

 zette, X, 428 (1885). 



Jeffrey (E. C). The Gametophyte of Botrychium Virgi- 

 nianum. Ann. Bot., XI, 481-486 (1897). 



Prantl (K.). Beitrage zur Systematik der Ophioglosseen. 

 \n Jahrb. des Kon. Bot. Garten (Berlin), III, 297-350 (1884). 



B. THE HORSE-TAILS. 



86. General Characters. — The horse-tails or scouring- 

 rushes belonging to the genus Equisetum are perennial, rush- 

 like plants, that may be found in damp, gravelly, or loamy soil, 

 some species even growing in shallow water. Our native species 

 vary in height from a few inches up to eleven feet, as seen 

 in some of the larger forms of E. robustum. In some species 

 only the root is perennial, the stems which are sent up for 

 producing fruit dying down to the ground every year. In others 

 the stems are evergreen, continuing through the winter. Some 

 species, like the common horse-tail (E. arvense), are dimorph- 

 ous, the fertile stems being simple and destitute of green color- 

 ing matter (chlorophyll), while the sterile stems are green 

 and copiously branched, The fertile stems of some other spe- 

 cies, as E. silvaticum, which are simple at first, after maturing 

 their fruit produce branches and resemble the ordinary sterile 

 stems (Figs. 21, 22). 



