American Species of Marchantia. 285 



of variability. There are, however, certain differences in the 

 epidermal cells and pores which deserve some emphasis. The 

 cells and pores are not only distinctly smaller than in M. domin- 

 gensis, but the pores are constructed on a simpler plan, the 

 opening being surrounded by fewer rows of cells and the number 

 of cells in each row being less subject to variation. The cells 

 bounding the inner opening tend to be more convex. It must 

 be admitted that these differences are very slight and might 

 not deserve much attention if they were not supported by other 

 differences derived from the female receptacle. 



The variability of the receptacles with respect to the number 

 of lobes has already been commented upon in connection with 

 the type specimen and becomes still more apparent from a study 

 of the published descriptions. According to Nees von Esenbeck 

 the usual number of lobes is seven, eight to ten being sometimes 

 present ; according to Spruce nine lobes are present in M. sub- 

 andina; according to Schiffner, who studied Raddi's specimen 

 in the Lindenberg herbarium, the normal number of lobes in 

 M. papillafa is six, a larger number being tmusual ; according 

 to Stephani both M. papillata and M. subandina have nine lobes 

 apiece. In the writer's opinion nine may be regarded as the 

 normal number of lobes, although a smaller number frequently 

 occurs. In the number of lobes, therefore, the species agrees on 

 the whole with M. domingensis. The receptacle, however, is 

 smaller; the lobes are more dilated and more frequently emargi- 

 nate at the apex ; the medium protuberance of the disc and the 

 convexity of the lobes are more pronounced; and the involucre is 

 less variable, being entire or nearly so and apparently never bear- 

 ing elongated teeth or cilia. Just how constant these differences 

 are can only be established by the study of more material. If they 

 should be found to intergrade it might become necessary to 

 reduce M. domingensis to synonymy under M. papillata, but the 

 differences seem sufficient at the present time to justify the 

 maintenance of both species as valid. 



The group of species to which M. domingensis and M. papil- 

 lata belong is well represented in paleotropic regions. Among 

 the species which are referable to this group M. emarginafa 

 R. Bl. & N.,^* M. linearis Lehm. & Lindenb.,^^ and M. Schaden- 



"* Nova Acta Acad. Caes.-Leop. Carol. 12 : 192. 1824. 

 ^ Lehmann, Pug. Plant. 4 : 8. 1832. 



