THE OFFICES OP THE PLANT 107 



2. The Plant in its Relation to Soil 



169. The plant is a soil maker. It breaks 

 down the rock by mechanical force and by dis- 

 solving some of its constituents (30, 306) . It 

 fills bogs and lagoons and extends the margins 

 of lakes and seas (32, 32a). 



170. The plant is a soil improver. It opens 

 and loosens hard soils, especially if, like the 

 clover, it has a tap-root, which it sends deep 

 into the earth. It fills and binds loose and 

 leachy soils. When it decays it adds humus 

 (33, 34, 73, 74). 



171. The plant is a soil protector. It pre- 

 vents the washing of soils, and protects the 

 sands of dunes and shores from the winds. 

 It holds the rainfall until it soaks into the 

 soil (70, 116). 



3. The Plant in its Relation to Climate 



172. The plant influences the moisture sup- 

 ply : by modifying the distribution of precipi- 

 tation ; by causing the retention of the pre- 

 cipitation ; by lessening evaporation ; by adding 

 moisture to the atmosphere. 



173. The plant influences the habitableness 

 of the earth by other means : as by modifying 

 extremes of temperature ; by affording wind- 



