xiv] 



THE FILAMENTOUS TYPE 



281 



The allied genus Hymenophyllum has branched prothalli consisting of 

 strap-shaped expanses one layer of cells in thickness, excepting at certain 

 marginal regions where they are thickened to several layers, thus forming 

 the archegoniophores. An extreme development after the manner seen in 

 Fig. 272, a, b, with marginal archegoniophores would account for what is 



Fig. 271. A — F, Trichomanes alatii/ii. A, B show the formation of a flattened prothallus from a 

 filament. C, relation of filaments to flattened expansions which bear sterigmata distally. D, sterig- 

 mata bearing gemmae. E, very young gemmae. F, mature gemmae detached, the lower beginning 

 to germinate. G, result of germination of gemmae of Trichomanes Kaulfussii. 



actually seen. The antheridia and archegonia are, however, borne together, 

 and they are directed downwards (Fig. 273). 



Von Goebel places in relation to these, which may well be held to be 

 flattened derivatives of a filamentous type of gametophyte, the irregularly 

 lobed prothalli of Vittaria {I.e. p. 958). They also consist of a single layer of 

 cells with marginal growth. At certain points that growth ceases, but the rest 

 of the margin continuing to grow produces very irregular lobes, suggesting 



