III. DESCRIPTION OF SPECIES 



Nees von Esenbeck^ divided the genus Marchantia into the two 

 sections Astromarchantia and Chlamidium. The first included 

 species in which the female peduncle was "central" ; the second, 

 which was first proposed by Corda as a genus, included species 

 in which the female receptacle was "excentric." In the first sec- 

 tion he placed M. polymorpha, in the second M. paleacea. These 

 two sections are retained in the Synopsis Hepaticarum, except 

 that the first is renamed Stellatae; they are likewise retained by 

 Dumortier,^ who coined the name Marchantiotypus for the first 

 section. Schiffner^ follows the example of the Synopsis, empha- 

 sizing the radial symmetry of the female receptacle in the Stella- 

 tae; while Stephani bases his two groups, "a" and "b," which 

 he does not designate by formal names, upon differences in the 

 symmetry of the female receptacle, the first group including spe- 

 cies with "symmetrical" receptacles and the second, species with 

 "unsymmetrical" receptacles. It is interesting to note that he 

 includes M. paleacea in his first group, although his predecessors 

 had placed it definitely in the section Chlamidium. 



The fact has already been brought out that the female recep- 

 tacles throughout the genus are always symmetrical with respect to 

 one plane of symmetry but never with respect to more than one. 

 Stephani's distinction, therefore, falls to the ground, and the dis- 

 tinction in the position of the stalk, emphasized by Nees von 

 Esenbeck, is not much more trustworthy. In certain species, 

 where the two basal rays are sometimes distinctly shorter than 

 the others and sometimes about as long, it breaks down alto- 

 gether; in the first case the stalk would be "excentric," in the 

 second "central." At the same time the sections Astromarchantia 

 and Chlamidium represent natural groups of species and can still 

 be maintained if different characters are used to distinguish 

 them. In Astromarchantia, for example, there are no sclerotic 

 cells in the thallus, and the rays of the female receptacle are 

 terete, at least in the outer part ; in Chlamidium, sclerotic cells 



^Naturg. Europ. Leberm. 4:60. 1838. 



'Bull. Soc. Bot. Belgique 13: 150. 1874. 



' Engler & Prantl, Nat. Pflanzenf am 1^ : 37- 1893. 



