302 PLANT LIFE. 



willows with the lowland forms. These latter are very 

 often tall and vigorous trees. The characteristic alpine 

 forms are extremely small, and, though woody and 

 perennial, have a straggling or trailing habit. Salix 

 lapponum, S. he7'baceiiin and 5. 7'epens are all of this 

 dwarf character, and the latter is very often only two or 

 three inches in height. This suppression of growth 

 probably depends on the exposure and the severe 

 climate. It has already been pointed out that in some 

 respects the seashore and the mountain tops have very 

 similar conditions. Along the sea-side, dwarf specimens 

 of shrubs and trees are very common, and they are 

 probably prevented from developing in the proper way 

 by the high winds, and possibly, also, by the large 

 amounts of salt in the soil. 



Bonnier has shown that alpine seedlings, when grown 

 under ordinary lowland conditions, are very different in 

 height, in general habit, and in appearance. This is of 

 course only what one would expect, as the six weeks of 

 an Alpine season cannot possibl}^ produce the same 

 luxuriance of vegetation as six or seven months in the 

 lowlands. 



The importance of the work of the Alpine plants lies 

 in their being able to exist on bare mountain rocks. 

 They thus supply the smaller Alpine streamlets with 

 the vegetable matter in the silt of which the small 

 streams often carry an extraordinary quantity. As 

 much as from 6.577 to 145.107 kilogrammes of silt 

 per cubic metre has been detected in an Alpine torrent. 



The coniferous belt and the intermediate stretches of 

 moorland and peatmoss have a similar important func- 

 tion ; but they are also sufficiently efficient as vegeta- 

 tion to pasture sheep, or to carry in places valuable forests 

 of Coniferous timber. 



