ii6 MOSSES AND FERNS chap. 



According to Leitgeb this is the case in several species of 

 Jungermannia, 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 pecuHar modifications observed in certain tropical 

 Hepaticae, 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 Protocephalosia ephemer aides, a species discovered by 

 Spruce in Venezuela, the plant forms a dense branching fila- 

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

 further resembles by having a subterranean 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 Lejunia metsgeriopsis, a 

 Javanese species discovered by Goebel growing upon the leaves 

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

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

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

 numerous multicellular gemmae. 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 Lejeunia, and from this three-sided 

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

 produced.^ 



Considerable variety is exhibited by the leaves of the 

 Acrogynse 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. Where 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 manjj^ 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 Buitenzorg Botanical Garden, vols. vii. and ix., 

 and in Flora, 1889 and 1893 



