122 PLANT-LIFE 



what lie is looking for, otherwise his search is not likely 

 to be successful. But there are species, such as Mar- 

 chantia and Pellia, which grow in large and conspicuous 

 patches in damp places, and can hardly be overlooked. 

 Liverworts do not form so well-defined a class as the 

 Mosses, and it is difficult to find one species which may 

 be regarded as typical; they occur in great variety of 

 form, and the class as a whole is so loose that grouping 

 into Orders is difficult. It may be said, however, that 

 in regard to outward appearance there are two groups: 

 (1) The Thallose Liverworts, in which the gametophyte 

 displays no distinction of stem and leaf; and (2) the 

 Foliose Liverworts, in which such a distinction is ap- 

 parent. The uninitiated observer might mistake the 

 foliose species for Mosses, but a little attention to detail 

 will yield knowledge of several points of distinction. 

 The leaves of the Foliose Liverworts display a somewhat 

 filmy appearance, and the whole plant, as a general rule, 

 has a " flat " mode of growth. With few exceptions, 

 Liverworts are dorsi-ventral— that is, they have upper 

 and lower surfaces, the former exposed to the light, the 

 latter facing the ground. The tissues are very simple, 

 and in many of the foliose kinds the green coloration is 

 extremely delicate. As to habitats, Liverworts are 

 moisture-loving plants and fond of a clean atmosphere; 

 this may also be said of Mosses, but not to the same 

 extent. Districts in which there is a heavy rainfall and 

 smoke-contamination is absent are favoured by Liver- 

 worts; they may be found growing in woods, on wet 

 banks, dripping rocks and walls, on the banks of shaded 

 streams, in the neighbourhood of waterfalls and cascades, 

 where they are spray-splashed and often submerged. 



