140 



FIG CULTURE 



tion is due to capillarity, not to gravity, and that 

 movement is most active in earth containing much 

 organic matter; notice how much faster a sponge 

 dries than substances of closer texture. Capillarity 

 is that power which lifts water from part to part 

 in a natural effort to maintain a pressure equilibri- 

 um, and as the surface dries the supply rises read- 

 ily from below. This process is continually going 

 on underground; as fig roots drink that close by, 

 removing it to branches, the quantity around them 

 is constantly reduced, and the rapidity of their 

 growth is dependent upon prompt renewals by 

 spongy organic matter. If soil is impervious — as 

 most new prairie ground — the supply is recuper- 

 ated slowly and all movements of tree life are pro- 

 portionately deliberate. In making fifty pounds 

 of wood ten tons of water is consumed and expired 

 by the leaves. If gravitational water percolates 

 through clay at the rate of one foot a week, how 

 much more slowly must capillarity act in bringing 

 a supply to root ends when the only impelling force 

 is the change of underground pressure caused by 

 absorptions through the membranes of microscopic 

 root tips. Add humus to clay soil and it is made 

 spongy and increases the activity of every, plant 

 produced. Alone, clay is difficult to work into a 

 pulverized top layer, but with organic matter 

 abundant, it makes the best surface mulch, readily 

 transmitting moisture from above and satisfactorily 

 conserving that below. 



