IV THE JUNGERMANNIACEJL 109 



to a disc, and the formation of a filament is completely sup- 

 pressed. This disc is nearly circular in outline, and at its edge 

 a single large cell appears (Fig. 51, B), whose relation to the 

 primary divisions of the spore is not quite clear. This cell 

 forms the starting-point for the growing apex of the gameto- 

 phore. As in the other forms, the first leaves are extremely 

 rudimentary, and only gradually is the complete gametophyte 

 developed. 



How far this variation in the form of the protonema is of 

 morphological importance is a question, as the same species 

 may show both a filamentous protonema and the discoid form. 

 According to Leitgeb this is the case in several species of 

 Jungermannia, and he suggests that the conditions under 



Fig. 51. — A, Germination of Lcjcunia scrpylli/olia ; B, young plant of Raduia ccitiplanata (Dum.) ; 

 .X, the apical cell (all the figures after Goebel). 



which germination takes place probably affect to a considerable 

 extent the form of the protonema. This is well known to be 

 the case in Ferns. 



The very peculiar modifications observed in certain tropical 

 Hepaticae, especially by Spruce and Goebel, should be 

 mentioned in this connection. In these forms the protonema 

 is permanent and the leafy gametophore only an appendage 

 to it. In ProtocepJialozia epheineroides, a species discovered by 

 Spruce in Venezuela, the plant forms a dense branching 

 filamentous protonema much like that of the true ]\Iosses, 

 which it further resembles by having a subterranean and an 

 aerial portion. Upon this confervoid protonema are borne the 

 leafy gametophores, which are small and appear simply as buds. 



