116 



EXPERIMENTS WITH PLANTS 



of a week. Which loses the most water; the least? 

 Explain. 



The result of cultivating the soil is to keep a layer 

 of loose, dry soil on top, which acts like the saw- 

 dust in preventing evaporation, by reason of the fact 

 that its large capillary spaces cannot take the water 

 from the smaller spaces of the underlying soil. This 

 is further illustrated by the fact that a dry brick will 

 take water from a moist sponge, but a dry sponge will 

 not take up water from a moist brick: it may be said 



that the surface crust 

 energetically draws 

 the water away from 

 the underlying soil, 

 just as a brick will 

 suck a sponge dry. 

 It is often noticed 

 that where the soil 

 has been well tilled 

 every wagon- track or 

 footprint remains 

 moist after the soil 

 around has become 

 dry, and weeds spring 

 up noticeably in such 

 places owing to the 

 fact that the com- 

 pressed soil maintains 



88a. New growth on Apricot trees growing side 

 by side. Above, the cultivated; below, the 

 uncultivated. 



