Haynes : The genus Sphaerocarpos 217 



mens from the same locality, Sphaerocarpos ' stipitattts Bisch. 

 replaces 5". Bertcrii Mont. (S. Berteroi of Stephani's Species 

 Hepaticarum). To the five species thus remaining from Stephani's 

 list, a sixth, the new species from the state of Washington, alluded 

 to at the outset of this paper, is added below. 



It should be remarked, perhaps, that Sphaerocarpos Notarisii, 

 Mont.* was, a few years after its publication, referred by Montagne 

 to its proper genus Riella. 



The species of Sphaerocarpos are certainly among the simplest 

 and most interesting of the Hepaticae and the importance of the 

 genus from the evolutionary and phylogenetic point of view is 

 clearly set forth in the following quotation from Professor Camp- 

 bell :f 



" 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 connec- 

 tion 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 de- 

 termine 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 specialized than that of Aneura or Sphaerocarpus. 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 condition 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 mid- 

 rib like Sphaerocarpus, three lines of development may be assumed to have arisen. In 

 one of these the differentiation was mainly in the tissues of the gametophyte, and the 

 sporophyte remained comparatively simple, although showing an advance in the more 

 specialized 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 rhizoid to the complex thallus of the mature gametophyte. In its 

 earlier phases it resembles closely the condition which is permanent in the simpler 

 anacrogynous Jungermanniaceae, 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 specialized thallus of the Marchantiaceae. Sphaerocarpus, showing as it does 

 points of affinity with both the lower Marchantiales and the anacrogynous Jungerman- 

 niales, probably represents more nearly than any other known form this hypothetical 

 type. Its sporogonium, however, simple as it is, is more perfect than that of Riccia, 

 and if our hypothesis is correct, the Marchantiales must have been derived from 

 Sphaerocarpus -like forms in which the sporophyte was still simpler than that of ex- 

 isting species. Assuming that this is correct, the further evolution of the Marchantiales 

 is simple enough, and the series of forms from the lowest to the highest very complete." 

 " In the second series, the Jungermanniales, starting with Sphaerocarpus, the line 

 leads through Aneura, Pellia, and similar simple thallose forms, to several types with 

 more or less perfect leaves — e. g., Blasia, Fossombronia, Treubia, Haplomitrium. 

 These do not constitute a single series, but have evidently developed independently, 

 and it is quite probable that the typical foliose Jungermanniaceae are not all to be traced 



*In De Not. Mem. R. Accad. Torino II. i : 343. /. d. 1-8. 1839. 

 f Campbell, D. H. The structure and development of mosses and ferns 157-159. 

 1905. [ed. 2.] 



