14 POPULAK, GEOGRAPHY OF PLANTS. 



ture, some of them six or seven inches high, others much 

 shorter, and covered with little catkins.* The plants which 

 have hitherto been named are such as we have examples of 

 at home in some species or another ; there are a few others 

 peculiar to the Polar zone, almost all of them Grasses. 

 There is a proportionate number of Cryptogamic plants ; of 

 Lichens there are nineteen species; one of these, called 

 Tripe de Roche, was for a long time the only food which 

 could be procured by Eranklin, Eichardson, and Back, 

 during their daring scientific researches. Such is the vege- 

 tation of the Polar zone. Amongst the obstacles which 

 prevent a richer development, we must remember, in addi- 

 tion to the temperature being through the greater part of 



* The Salix herlacea is also found on the sharp declivities of the Alps, 

 under circumstances which exert a peculiar influence on the manner of its 

 growth. It not unfrequently happens, that the soil on the steep mountain- 

 sides, when moistened with rain, gives way, and covers up both the woody, 

 creeping stems, and the leaves which grow in pairs at their extremities. From 

 the axils of each separate pair of leaves, thus suddenly buried alive, two more 

 diverging branches, each terminating in another pair of leaves, are then de- 

 veloped, which force their way upwards to the air, through the earth which 

 has been heaped upon the plant. As this process is repeated every time a 

 fresh deposit of the soil is washed down by the rain, one plant, by thus 

 multiplying itself in a geometrical ratio, soon covers a wide surface; the 

 woody underground branches in this manner attaining an extraordinary length. 



