IV THE JUNGERMANNIACE^ 113 



latter (Fig. 52, B) the gemma is a nearly circular cell plate 

 attached to the surface of the leaf by a stalk composed of a 

 single cell. The first wall in the young gemma divides it into 

 two nearly equal cells, in each of which a two-sided apical cell 

 is formed, so that like the gemma of Mardiantia there are two 

 growing points. There are usually four cells that differ from 

 the others in their thicker walls and projecting on either side 

 of the gemma above the level of the other cells. These serve 

 as organs of attachment, perhaps by the secretion of mucilage, 

 and by them the young plant adheres to- the surface of the 

 fern leaf upon which it grows. The development of the 

 gemmae, whether unicellular or multicellular, follows very closely 

 that of the germinating spores. 



Classification of the Jungermanniacecs AcrogyncB 



In attempting to classify this immense family, great 

 difficulties are encountered. While they show a considerable 

 amount of variation, the differences are not constant, and the 

 forms merge so one into another that a satisfactory subdivision 

 of the group seems almost hopeless. In regard to essential 

 characters, such as the growth of the stem, origin and structure 

 of the sexual organs and sporogonium, they show remarkable 

 uniformity, and evidently constitute a most natural group, 

 allied very closely to the anacrogynous forms, as we have 

 already attempted to show. The latest attempt to classify 

 them is that of Schiffner,^ who confesses how difficult, perhaps 

 impossible, a satisfactory arrangement is. He proposes eight 

 subdivisions, as follows : I. Epigoniantheae ; IL Trigonantheae ; 

 III. Ptilidioideae ; IV. Scapanioideae ; V. Stephaninoideae ; VI. 

 Pleurozioideae ; VII. Bellincinioideae ; VIII. Jubuloideae. 



^ Schiffner (l), p. 22. 



