82 VASCULAR CRYPTOGAMS 



climbing habit. The number of species which are at the present time 

 applied to any economical purpose is extremely small. The common 

 brake, Pteris aquilina, is largely used throughout Northern Europe for 

 forage purposes, and for the stuffing of rough beds and pillows. The so- 

 called ' male fern,' Aspidium filix-mas, has a very ancient repute as a 

 vermifuge, and is still occasionally employed for that purpose, as also are 

 several other species to a less extent in different parts of the globe, either 

 for a similar purpose or as astringents and mucilages. In several species, 

 especially tropical, the stem contains sufficient starch to be esculent. 

 The number of known species of ferns is at present estimated at about 

 3,000, but it is constantly and rapidly increasing. They are arranged in 

 a comparatively small number of genera, the limits of which are often 

 extremely difficult to define. 



Literature. 



Mettenius — Filices Hort. Bot. Lipsiensis, 1856. 



Hofmeister — Abhandl. Sachs. Gesell. Wiss., vol. v., 1857; and Pringsheim's Jahrb. 



wiss. Bot., 1863, p. 278. 

 Wigand — Botanische Untersuchungen, 1854. 

 Newman — History of British Ferns, 4th ed. , 1865. 

 Reess^(Sporange) Pringsheim's Jahrb. wiss. Bot., 1867, p. 217. 

 Strasburger — (Fertilisation) ibid., 1869, p. 390. 

 Kny— (Antherid) Monber. Akad. Wiss. Berhn, 1869, p. 416 ; and Pringsheim's 



Jahrb. wiss. Bot., 1869, p. I. 

 Hooker and Baker — Synopsis Filicum, 1868. 



Goebel — (Prothallium of Gymnogramme) Bot. Zeit., 1877, pp. 671 et seq. 

 Weiss — (Bundle-sheath) Flora, 1880, p. 119. 

 Cramer — (Fertilisation) Denkschr. Schweiz. Naturf. Gesell., 1880. 

 Haberlandt — (Vascular Bundles) Sitzber. Akad. Wiss. Wien, Ixxxiv., 1881, p. I2I. 

 Lachmann— (Root-organs) Compt. Rend., xcviii., 1884, p. 833 ; and ci., 1885, p. 592. 

 Klein— Bot. Zeit., 1884, pp. 577 et seq. 



Schmidt — (Dehiscence of Sporange) Flora, 1885, pp. 451, 471, and 1887, pp. 177, 

 202; and Ber. Deutsch. Bot. Ges., 1886, p. 396. 



Campbell— (Prothallium) Bot. Gazette, 1885, p. 355. 



Thomae— (Leaf-stalk) Pringsheim's Jahrb. wiss. Bot., 1886, p. 99. 



Goebeler — (Pales) Flora, 1886, pp. 451 et seq. 



Gardiner and Ito — (Mucilage-cells) Ann. of Bot., i., 1887, p. 27. 



Campbell — (Struthiopteris germanica) Mem. Boston Soc. Nat. Hist., 1887, p. 17. 



Klindig — (Sporange) Hedwigia, 1888, p. I. 



The following classification of the Filices into families or orders 

 follows partly the plan proposed by Mettenius, partly that adopted in 

 Hooker and Baker's ' Synopsis Filicum.' It must, however, be distinctly 

 borne in mind that the divisions are of very unequal value. The first 

 three are closely allied to one another ; the Hymenophyllacese show con- 



