The Root and the Soi. 71 
104. The Branching of Roots, in land plants, appears. 
to depend much upon the amount of free oxygen (31) and 
available plant food the soil contains, so long as the moist- 
ure supply is sufficient. In cultivated grounds, the roots 
of crops usually branch most freely just at the bottom of 
the layer of soil stirred by the plow, this being the point at 
which the supply of oxygen, plant food and moisture are~ 
probably best suited to root growth. As the depth of till- 
age is increased, roots branch freely at a greater depth. 
Masses of decomposed manure, beneath the surface of the 
soil, are usually penetrated through and through with finely 
branched roots; and fragments of bone in the soil are often 
inclosed in a mat of delicate rootlets. These materials fur- 
nish plant food in abundance. Roots that penetrate the 
deeper and more compact layers of soil, on the other hand, 
and those in poor and dry soils, are comparatively little 
branched. It is clear, therefore, that unless a soil is well 
aerated (94) by a proper system of tillage, and by draining 
if need be, and unless it contains abundant soluble plant 
food in the aerated part, the roots 
of plants growing upon it will not 
branch freely and hence the plants. 
cannot be well nourished. 
105. Transplanting (400) 
and Root Pruning (416) Stimu= 
late Root Branching. Removing 
the terminal growing points of 
either the stem or root stimulates 
the development of other growing 
Fru. 29. Snowing how root points farther back. Transplanting 
pruning stimulates root branch- 
ing. or root pruning accomplishes this 
