ii6 MOSSES AND FERNS chap. 



According to Leitgeb this is the case in several species of 

 Jnngcnnannia, and he suggests that the conditions under 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 

 HepaticcT, especially by Spruce and Goebel, should be men- 

 tioned in this connection. In these forms the protonema is 

 permanent and the leafy gametophore only an appendage to it. 

 In Protoccphalo::ia cphcnicroidcs, a species discovered by 

 Spruce in A'enezuela, the plant forms a dense branching fila- 

 mentous protonema much like that of the true Mosses, which it 

 further resembles by having a sul^terranean and an aerial por- 

 tion. Upon this confervoid protonema are borne the leafy 

 gametophores, which are small and appear simply as buds. 

 Among the other remarkable forms is Lcjiinia mctzgcriopsis, a 

 Javanese species discovered by Goebel growing upon the leaves 

 of various epiphytic Ferns. It has a thallus much like that of 

 Mctzcgcria, and like it has a two-sided apical cell. This thallus 

 branches extensively (Fig. 60, A), and propagates itself by 

 numerous multicellular gemmse. This thallose condition is, 

 however, only maintained during its vegetative existence. 

 Previous to the formation of the sexual organs, the two-sided 

 apical cell of a branch becomes three-sided, as in the young 

 plant of other species of Lcjcuuia, and from this three-sided 

 apical cell a short leafy branch, bearing the sexual organs, is 

 produced.^ 



Consideral:ile variety is exhibited by the leaves of the 

 Acrogyucx as to their form and position, but all agree in their 

 essential structure and early growth. The two lobes may be 

 either equal in size or unequal. In the latter case either 

 the dorsal or ventral lobe may be the larger, when the leaves 

 are overlapping, as occurs in most genera. \Miere the dorsal 

 half is the larger it covers the ventral lobe of the leaf in front 

 of it, and the leaves are said to be "incubous" ; where the 

 reverse is the case, the leaves are "succubous." These differ- 

 ences are of some importance in classification. 



In many species, especially the tropical epiphytic forms, one 



lobe of the leaf frequently forms a sac-like organ, which ap- 



* For a complete account of these forms as well as others, see Goebel's 

 papers in the Annals of the Buitcncorg Botanical Garden, vols. vii. and ix., 

 and in Flora, 1889 and 1893 



