36: 



MOSSES AND FERNS 



CHAP. 



prothallia from branches of the filamentous forms, and 

 Hynnenophyllum always has a flat hepatic-like prothallium, which 

 in its earlier stages, according to Sadebeck,-^ always develops a 

 two-sided apical cell, and differs in no wise from that of other 

 Ferns. These prothallia, however, remain single - layered 

 throughout, although they reach an extraordinarily large size, 

 and branch much more freely than those of any other Ferns 

 (Fig. 187). The root-hairs are always very short and dark- 



FiG. iS 



-Hymenophyllum isp). Margin of a prothallium with numerous gemmse k; X 85 ; 

 B, a young gemma, X260; st, its stalk. 



coloured, and generally occur in groups upon the margin only. 

 The branching of the prothallia is either monopodial or 

 dichotomous, and the latter method may be repeated a number 

 of times. They may live for an indefinite time apparently. 

 The writer has kept prothallia of both TricJiomanes and 

 HymenopJiyllinn for nearly two years, at the end of which time 

 they showed no diminution of vigour. 



They form ordinary adventitious shoots, but there are also 



^ Sadebeck (6), p. 161. 



