The Root and the Soil. 73 



of the plant should, therefore, be aimed at promoting the 

 formation of root- tips. In other words, we should encour- 

 age root branching. * How may we do this ? 



104. The Branching of Roots in land plants appears to 

 depend much upon the amount of free oxygen (31) and 

 available plant food which the soil contains, so long as 

 the moisture supply is sufficient. In cultivated grounds 

 having a compact sub-soil the roots of annual crops 

 usually branch most freely just at the bottom of, or a 

 little below, 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 tillage 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 

 CA roots: and fragments of bone in 



*t 



the soil are often inclosed in a 

 mat of delicate rootlets. These 

 materials furnish 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 usually little branched. It is 

 _ clear, therefore, that unless a 



FIG. 31. showing how root S oil is well aerated (94) by a 



pruning stimulates root 



branching. proper system of tillage, and by 



* Root branches must not be confounded with root-hairs. In Fig. 28, 

 branches of the roots appear at e. e. e. The branches bear root^hairs when 

 of sufficient length, but root-hairs never develop into branches. 

 5 



