74 Principles of Plant Culture. 



102. Only the Youngest Parts of Roots are Active 

 in Absorption. The part from which the root-hairs 

 have perished absorbs little water, but is chiefly useful 

 in giving strength to the plant and in conducting the 

 plant fluids. The absorbing part of any given rootlet 

 is, therefore, comparatively short. It follows that the 

 amount of nourishment a given plant can receive will 

 depend upon the number of its root-tips. Our treat- 

 ment of the plant should, therefore, be aimed at pro- 

 moting the formation of root-tips. In other words, we 

 should encourage root branching.* How can we do 

 this? 



103. 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 ground 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 

 FIG. si. showing how supply of oxygen, plant food 



root pruning stimuates -, , , i i T_ 



root branching. and moisture are probably best 



suited to root growth. As the depth of tillage is in- 

 creased, roots branch freely at a greater depth. Masses 



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

 *ig. 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. 



