136 



FIG CULTURE 



This estimate was based upon weights after a 

 good rain, and very clearly shows one of the chief 

 functions of humus. Humus is even more essen- 

 tial in light soil than with clay, or silt lands, for, 

 while in the latter case it percolates more rapidly 

 by the addition of humus, in the former instance 

 the moisture retention is poor and it becomes 

 necessary as a means to avoid the rapid fluctua- 

 tions that follow changes of weather; without 

 humus our sandy loams fail to respond reliably 

 to tillage, and change beyond all control in their 

 plant producing power. With a million root 

 hairs on every tree straining the moisture into 

 its circulatory system the water content is soon 

 reduced, and when it becomes less than twelve 

 per cent fig trees are unable to grow. If the 

 soil is entirely filled with water it is non-pro- 

 ductive, and as, ordinarily tw T enty-five per cent is 

 the maximum quantity of water it will retain, un- 

 less organic matter exists in considerable propor- 

 tion, there is only a margin between twelve and 

 twenty-five per cent when cultivated trees will 

 grow. 



A convenient division of soil water is sometimes 

 made by calling that which passes downward in 

 drainage gravitational, being moved by gravity; 

 that remaining in the interstices capillary water, 

 as it moves up and down and somewhat laterally 

 wherever capilarity exists; and those tiny films 



