THE PHILOSOPHY OF FARMING. 587 
into action—and more material into that extended 
space. And as the roots take in the material, 
for the fluid within the plant to carry forward— 
as they extend and increase in the midst of an 
extended supply of material—growth ensues 
apace—just as, when in a building more hands 
are employed, and more material brought to 
work upon, the building rises with greater 
rapidity. 
This great physiological truth in vegetation is 
substantiated by every fact which we observe in 
the economy of growth. In gravelly and sandy 
subsoils trees thrive luxuriantly. The same kinds 
are stunted and meagre, on stiff clayey substrata, 
and impervious subsoils. In the former, the 
roots are found to extend deep and wide. In 
the latter, downwards they cannot get, and, there- 
fore, are checked and restrained in their growth. 
Trees near farm buildings and sewers, in stiff 
clayey soils, also thrive better than in hedge- 
rows, because their roots can extend along the 
sides of the foundations of the buildings, and 
along the sewers, where air circulates, and thence 
obtain larger supplies. And the remarkable 
changes which always follow drainage on lands 
which have been swamped—not only in the quan- 
