Roots loi 



We speak commonly of the air as being **damp" or 

 **dry, " as the case may be; but in point of fact it is 

 never absolutely dry, for nothing could live in it if it were. 

 It always contains some amount of watery vapor, and 

 whether it be large or small, soil which has been dried 

 during the day regains some degree of moisture by night 

 by the simple process of sucking it from the air. The 

 air sucks it from the soil by day, especially during sun- 

 shine or dry wind, and the soil thus dried sucks it back 

 again at night. 



Some soils suck much more moisture from the air than 

 others, and some are also able to keep it much longer 

 than others. We all know that a sandy soil, for instance, 

 is a dry soil: it takes some time to grow really damp, and 

 it dries again very quickly. Indeed, pure quartz-sand 

 seems as if it could not be moistened by anything short of 

 rain or dew, being incapable of sucking any moisture from 

 the very dampest air. 



A chalk or limestone soil, on the other hand, acts like 

 a sponge, and though it may dry on the surface, keeps 

 its moisture a long time within. The subsoil of the Kala- 

 hari Desert, already mentioned, is limestone; and this is 

 probably one reason why the grass there is able to remain 

 green so long without rain. Such water as is received is 

 kept for some time, stored up in the subsoil. 



Of all kinds of soils, it is those containing most vege- 

 table matter which take up most moisture, and also remain 

 damp the longest. 



It is a curious fact, however, that the soils which are 

 least ready to part with their moisture to the air are also 

 those which are least ready to part with it to the roots of 

 plants. There may be actually more moisture in vege- 



