V THE ANTHOCEROTEyE 149 



of the capsule is unlimited. All that is needed to make the 

 sporophyte entirely independent is a root connecting it with 

 the earth. 



TJie Inter-relationsJiips of tJie Hepaticce 



From a review of the preceding account of the Liverworts, 

 it will be apparent that these plants, especially the thallose 

 forms, constitute a very ill-defined group of organisms, one set 

 of forms merging into another by almost insensible gradations, 

 and this is not only true among themselves, but applies also 

 to some extent to their connection with the Mosses and 

 Pteridophytes. The fact that the degree of development of 

 gametophyte and sporophyte does not always correspond makes 

 it very difficult to determine which forms are to be regarded as 

 the most primitive. Thus while Riccia is unquestionably the 

 simplest as regards the sporophyte, the gametophyte is very 

 much more specialised than that of Aneura or SpJicerocarpus . 

 The latter is, perhaps, on the whole the simplest form we know, 

 and we can easily see how from similar forms all of the other 

 groups may have developed. The frequent recurrence of the 

 two-sided apical cell, either as a temporary or permanent con- 

 dition in so many forms, makes it probable that the primitive 

 form had this type of apical cell. From this hypothetical form, 

 in which the thallus was either a single layer of cells or with an 

 imperfect midrib like SpJicerocarptis, three lines of development 

 may be assumed to have arisen. In one of these the differenti- 

 ation was mainly in the tissues of the gametophyte, and the 

 sporophyte remained comparatively simple, although showing 

 an advance in the more specialised forms. The evolution of 

 this type is illustrated in the germinating spores of the 

 Marchantiaceae, where there is a transition from the simple 

 thallus with its single apical cell and smooth rhizoids to the 

 complex thallus of the mature gametophyte. In its earlier 

 phases it resembles closely the condition which is permanent in 

 the simpler anacrogynous Jungermanniacese, and it seems more 

 probable that forms like these are primitive than that they 

 have been derived by a reduction of the tissues from the more 

 specialised thallus of the Marchantiaceae. SpJicerocarpus, 

 showing as it does points of affinity with both the lower 

 Marchantiaceae and the anacrogynous Jungermanniaceae, 

 probably represents more nearly than any other known form 



