138 FIG CULTURE 



to the dilution of soil solutions until too thin to sus- 

 tain life, or if from want of aeration, or whether 

 plant stagnation takes place at this point by reason 

 of noxious denitrifying bacteria, there being con- 



The cut illustrates how particles of sand (magnified) can be so 

 mixed with humus that otherwise sterile soil is built up into a 

 fertile condition. In this way organic matter becomes useful to 

 conserve moisture and prevent too much circulation of air. 



flicting theories about the causes. But we all know 

 that orchard trees will soon die if gravitational wa- 

 ter envelopes their roots. Then the problem of 

 drainage is primarily to provide an outlet for gravi- 

 tational water, as well as to enlarge the capacity of 



