XLVIl] 



PROTHALLI 



245 



certain Hymenophyllaceae (Fig. 745). This may not improbably be a 

 specialisation in both in relation to the epiphytic habit. The sexual organs, 

 however, do not diverge from the standardised Leptosporangiate type. 



Fig- 745. Gametophyte of Vittarieae. A-K, the prothallus of Vitiaria lineaia (L.) Sm. (after 

 Britten and Taylor). A, lower surface of prothallus. B, prothallus with eleven growing points. 

 C, lobe of prothallus bearing gemmae. D, margin of prothallus with sterigmata. E, a gemiiia. F, a 

 gemma with two withered antheridia {a, a) and a young prothallus from the margin of which three 

 others have arisen. ( x 25.) G, young prothallus arising from the margin of an old one. (x8o.) 

 H, young prothallus with three growing points arising from a single cell of an old prothallus. ( x 16.) 

 /, underside of a lobe of a prothallus bearing archegonia. / and K, antheridia. ( x 140.) L and M, 

 the prothallus of Hecistopteris piimila (Spr.) J. Sm. (after Goebel). L, 1, prothallus with gemma- 

 bearing lobes {Br)) and adventitious prothalli (.J, A) ; 2, sterigma {S) and young gemmae {Br. i and 

 Br. 1). HI, I, mature gemma; 2 and 3, gemmae which have formed young prothalli ; 4, gemma, the 

 end cells of which have grown out into short rhizoids. (After Williams, from authors quoted.) 



