162 THE PRINCIPLES OF PRUNING 



parts tend to thicken rather than to elongate. We 

 are already prepared for these assertions from 

 the study of girdling (Figs. 95, 96, 97, 107). 



A complete obstruction amounts to a severing 

 of the shoot or heading- in ; and we have already 

 found (Section 9) that heading -in tends to de- 

 velop strong growths from the lateral buds. The 

 common methods of obstructing the movements 

 of sap are by girdling or ringing, notching, and 

 bending or twisting the shoot. Girdling by the re- 

 moval of bark, however, is such a complete ob- 

 struction as to starve the part below the girdle, 

 and the statements which may be made concern- 

 ing its effects do not always apply to notching and 

 bending the shoot. (See discussion in Chap. V.) 



It should be remembered that the upward move- 

 ment of sap takes place in the young or sap- 

 wood, and a notch only through the bark does 

 not directly affect this movement. The downward 

 movement takes place in the inner bark, or bast, 

 and a notch only through the bark is, therefore, 

 able to check it. A notch through both the bark 

 and sapwood cuts off both movements and is equiv- 

 alent, in this respect, to cutting off the shoot. 



11. Checking groivth, so long as the plant re- 

 mains strong and healthy, induces fruitful- 

 ness. 



Very strong growth is usually at the expense of 

 fruit -bearing. Tilling and manuring may be 



