122 FIELD, FOREST AND FARM 



even more than pinching, to promote the desired 

 growth of the weak part. The more branches we 

 suppress entirely, the fewer will be left to share the 

 sap needed by the branches we wish to strengthen. 



"What turns aside the sap from the part pruned, 

 pinched, or nipped, toward the part left intact, is 

 evidently the more or less complete suppression of 

 foliage. It is primarily the leaves that by the con- 

 tinual evaporation of which their surface is the seat 

 determine the ascent of the liquid drawn from the 

 soil by the roots. The more numerous these leaves 

 are at any one point, the more abundant the flow of 

 sap to that point; the scarcer they are, the less the 

 flow of sap. To diminish at any point the number of 

 leaves by pinching, bud-nipping, or any other means, 

 is therefore to diminish at the same point the flow 

 of sap, which will go in some other direction, to the 

 parts that have more leaves and hence a more rapid 

 rate of evaporation to summon the sap. It is plain, 

 then, that a middle course may be followed between 

 the pinching that partly suppresses the foliage of a 

 young branch and the bud-nipping that suppresses it 

 entirely. This middle course consists in cutting a 

 certain number of leaves from the too vigorous 

 shoots; and they should be cut clean without tear- 

 ing, by severing the stem and leaving its base un- 

 disturbed. 



"The easiest way for the sap to run from the 

 roots to the foliage is from bottom to top in a ver- 

 tical line. Anything that interferes with this course 

 hinders also the upward impetus. Thus in branches 



