23° Alexander W. Evans, 



are normally present in the thallus, and the rays of the female 

 receptacle are flat or convex. In both these sections the invo- 

 lucres (and clusters of archegonia) alternate with the rays. 

 A third group, typified by M. geminata, in which the involucres 

 are situated beneath the rays, also seems worthy of sectional rank, 

 but since this group is not represented in America (at any rate 

 according to our present knowledge), it need not be further 

 considered here. 



In the preparation of this paper the writer has had the privi- 

 lege of examining the large collection of Marchantiae in the 

 herbarium of the New York Botanical Garden (N. Y.),* which 

 includes the Mitten and Underwood herbaria. This has been 

 supplemented by the specimens in the Cryptogamic Herbarium 

 of Harvard University (H.), which includes the Taylor and 

 Sullivant herbaria, and by the material in the United States 

 National Herbarium (U. S.), the private herbarium of Miss 

 C. C. Haynes (C. C. H.), and the herbaria at Yale Univer- 

 sity (Y.), the last including the Eaton herbarium and the writer's 

 private herbarium. Several specimens from the Montagne (M.) 

 and Boissier (B.) herbaria, including a number of types, have 

 likewise been available for study, through the courtesy of MM. 

 Paul Hariot and G. Beauverd, respectively. The writer would 

 extend his sincere thanks to all who have aided him in his work. 



Key to the species 

 Thallus destitute of sclerotic cells : stalk of male receptacle destitute of 

 air-chambers, with two rhizoid-furrows ; rays short and broad: stalk 

 of female receptacle with a single band of air-chambers and two 

 rhizoid-furrows; rays mostly nine or more, terete, at least in outer 

 part ; involucre with dentate or ciliate lobes : cupules with dentate 

 lobes, bearing papillae on outside. 



Section I. Astromarchantia. 

 Epidermal pores usually surrounded by four rows of cells, never dis- 

 tinctly cruciate: marginal scales present; appendages of median 

 scales irregularly crenulate or denticulate. 

 Rays of female receptacle bearing papillae; basal sinus scarcely or 

 not at all wider than the others. 



1. M. polymorpha. 



Rays of female receptacle destitute of papillae; basal sinus usually 



distinctly wider than the others. 



2. M. plicate. 



* The letters in parentheses are abbreviations used below in the citation 

 of specimens. 



