64 VASCULAR CRYPTOGAMS 



Fankhauser (Prothallium) Bot. Zeit., 1873, p. i. 



Strasburger Bot. Zeit., 1873, pp. 81 et seq. 



Bruchmann Ueb. Wurzeln v. Lycopodium u. Isoetes, 1874. 



Beck (Prothallium) Oesterr. Bot. Zeitschr., 1880, p. 341. 



Bertrand (Psilotum) Compt. Rend., xcvi., 1883, pp. 390,518; (Phylloglossum) do., 



xcvii., 1883, pp. tp^et seq. 

 Solms-Laubach (Psilotum) Ann. Jard. Bot. Buitenzorg, 1884, p. 139, and 1886, 



pp. 217, 233. 

 Treub (Prothallium) Ann. Jard. Bot. Buitenzorg, 1884, p. 307, and 1886, p. 87; 



see Nature, xxxi., 1885, p. 317, and xxxiv., 1886, p. 145. 

 Galloway (Spores) Bull. Torrey Bot. Club, 1885, p. 55. 

 Bower (Phylloglossum) Proc. Roy. Soc., xxxviii., 1885, p. 445. 

 Bruchmann (do.) Bot. Centralbl., xxi., 1885, pp. 23, 309. 

 Treub (Prothallium) Ann. of Bot., i., 1887, p. 119. 

 Goebel (Prothallium) Bot. Zeit., 1887, pp. 161, 177. 



Class IV. Filices. 



Ferns (under which term the Ophioglossaceae are also included in 

 popular language) are by far the most numerous and best known class 

 of Vascular Cryptogams. In some families, however, as the Marattia- 

 ceae and Schizaeaceae, much yet remains to be made out with regard to 

 the history of development, and their exact position in the -N circle of 

 affinity must remain for a time doubtful. 



The germinating spore develops into the prothallium by the burst- 

 ing of the cuticularised exospore, and the rapid growth and division of 

 the contents of the endospore into a plate of cells. Before germination 

 the contents of the spore become invested with a new cellulose mem- 

 brane. But the tabular prothallium does not always result directly from 

 the contents of the spore. In the Hymenophyllaceae the spore under- 

 goes division, even before the rupture of the exospore, into three cells, 

 one of which only attains great development, dividing by transverse 

 septa, and branching until it greatly resembles the protoneme of a 

 moss ; the flat prothallia then springing from lateral shoots. In most 

 of the Polypodiaceae, which include by far the greater number of the 

 genera of ferns, and in the Schizaeaceae, the contents of the spore 

 develop directly into a short segmented filiform protonemal structure, 

 which expands at the apex into a cordate or reniform plate of tissue, 

 consisting at first of only a single layer of cells. If a single apical cell 

 is present, it soon disappears, and is replaced by a growing point situated 

 in a depression at the anterior end of the prothallium, behind which a 

 cushion, several layers in thickness, is formed by tangential cell- 



