2 INTRODUCTION. 



sometimes frondose — that is to say, the stem and 

 leaves are combined in a flat prostrate frond, which 

 lies flat upon the matrix. The foliaceous Hepaticae 

 moreover have their leaves of a thinner and more 

 delicate substance, and are destitute of a distinct 

 central midrib. Finally, the Hepaticae usually 

 contain within the fruit capsule, intermixed with 

 the spores, elongated spiral fibres, called elaters^ 

 which are absent from true Mosses. These are the 

 most evident general distinctions which are relied 

 upon in the discrimination of the two groups. 



The entire group of Hepatic^ are subdivided 

 into four natural orders, which have each their 

 peculiar character. These are the Marchantiacece^ 

 which are frondose, and have the sporangia disposed 

 on the under side of stalked receptacles, the spores 

 being mixed with elaters ; this is accepted generally 

 as the highest order of Liverworts. Then follow 

 \\\Q. JimgcrmanniacecB^ in which the fruit is pedun- 

 culate and solitary, the sporangium when mature 

 splitting into four equal valves, and the spores 

 mixed with elaters. After these are the Ricciacece^ 

 the species of which are frondose, with the sporangia 

 sunk into the substance of the frond, or borne upon 

 the surface, and the spores unmixed with elaters. 

 Finally the A^ttJiocerotacece^ in which, although the 

 vegetation is frondose, the sporangium is exserted 

 and erect, splitting longitudinally on one or both 

 sides,and exhibiting a thread-like central columella. 

 The elaters, when present, elementary and imperfect. 

 Of all these the most abundant in species is the 

 Juiigeniianuiacece, which includes far more than the 



