262 PLANT LIFE. 



diuni tamariscinum. Horizontal branches in a very 

 moist wood, boulders by a stream, and the roots and 

 lower part of the tree trunks are all specially favourite 

 situations for the growth of mosses. Sometimes they 

 grow only on those parts of a trunk which are kept 

 moist by the rain water trickling down from above. 

 In specially favoured positions, however, the trees will 

 often show a very complex moss flora on their barks. 

 Patches of this bark flora will be found on examination 

 to consist of many different kinds of mosses, liverworts, 

 lichens, and sometimes of fungi and algae in addition. 

 Probably these plant groups are in some degree depen- 

 dent upon one another for their existence ; but their 

 precise relations have not as yet been determined. 

 Amongst the most characteristic of these bark mosses are 

 Hypnuni cupressiforine, and the most conspicuous of 

 the Liverworts is the dark reddish-brown Frullania 

 tainariscini. 



But it is not only in the peat bogs and in the moist 

 atmosphere of woods that mosses are to be found. 

 Many mosses occur in very dry and exposed places, 

 where drought, wind, and sunshine alternate with mists, 

 heavy rain, and severe cold. Mosses are, as a rule, 

 very tenacious of life. They dry up easily, and some 

 can be kept dry for over thirty years without losing the 

 power of becoming fresh and green when they are again 

 exposed to moisture. Thus, a dry and withered-look- 

 ing moss tuft may be torn away by the wind and 

 blown a very long distance without injury. If it 

 comes to rest in a favourable situation it will throw 

 out its root hairs, and proceed to grow. Many of 

 the mosses have also very distinct arrangements for 

 adapting themselves to periods of drought and ex- 

 posure. The leaves of Polytrichum, of Rhacomitrium, 



