2 54 PLANT LIFE. 



independent of the ground and floats upon the water 

 Hke Lemna or the Florida Hyacinth. Other specialised 

 mosses are found on dry-stone walls, on tree trunks 

 and branches by the seaside ; and in the tropics special 

 forms occur in great abundance, and extraordinary 

 variety. Even screes of rolling stones are often attacked 

 by a few mosses. There is, in fact, scarcely one single 

 vegetation in which mosses are absolutely wanting. 

 Yet it is only in the peat, in the barren tundras of 

 Siberia, Arctic Canada and Europe, and perhaps 

 towards the summits of alpine rocks that they can be 

 considered as of first importance. In all other positions 

 they have a subordinate part to play the exact nature 

 of which has not yet been made quite evident. 



They are never tall plants. The largest species have 

 a prostrate, branching habit ; but scarcely any are more 

 than a few inches in height. This, however, depends 

 upon a very simple peculiarity in the stems. Whereas 

 ferns and flowering plants are able, in every case, to 

 raise water within the stems, mosses and liverworts are 

 without an efficient vascular tissue, and most of the 

 water ascends on the outside of the stem. The leaves 

 are small and numerous ; and along with certain special 

 hairs which are found on the outside, form capillary 

 passages by which the water rises. Such a method 

 can only be employed with low-growing closely-set 

 plants. It is utterly unsuitable for tall erect species. 

 This has been well expressed in the following " verses " 

 by Carl Schimper : 



Empfindlich fiir das feuchte 



Wie fiir des ortes Leuchte 



Was Wurz' und Stengel leisten 



Gleich siehst du bei den meisten 



Was die g-eheim auch mischen, 



Sie konnen nicht erfrischen 



