J 2 TRANSACTIONS OF ROVAL SCOTTISH ARBORICULTURAL SOCIETY. 



The plane tree in youth naturally develops an exuberance of 

 primary lateral branches on its stem, and there is a contest 

 for leadership amongst them at the top. No one of these 

 branches continues its growth by a terminal bud — a feature 

 of other trees also — lime, elm, for instance. Arrest and self- 

 pruning of the tip takes place, and the elongation of the shoots 

 proceeds from lateral buds nearer to, or farther from, the primary 

 tip. The continuation bud may be the one immediately behind 

 the point of abscission of the shoot tip, but often the shoot dies 

 back to some distance behind the normal abscission line of self- 

 pruning, and thus the elongation of a shoot in any one season 

 is no measure of the permanent addition in length that is to 

 be made to the axis, whether terminal or lateral, of which it 

 is a part, for only the base of the annual growth may survive. 

 If the tree grows freely without natural or artificial curtailment 

 and discipline a relatively heavy brushhead is formed of intricate 

 zig-zag branches of which the terminations may — many of them 

 — be dead. In consequence : — 



1. The surface exposed to air currents is large, and by 



so much increases the risk of overturn and of damage 

 by rending in open situations. 



2. Many of the primary branches do not survive in whole 



or in part the struggle for air and light with their 

 fellows, and become, therefore, an encumbrance 

 through their interference with the development and 

 leafage of the branches that are ultimately successful, 

 and they may be even a danger to the tree as 

 starting-points for disease. 



3. The upward growth of the whole tree is retarded through 



the demand made by the surplusage of lower 



branches, and there is apt to be forking and division 



of the main trunk. 



In rich soil these features are naturally exaggerated, and 



along with this goes this further character, that the wood which 



is formed is less resistant to lateral strain, and is, therefore, 



more liable to damage by breaking. 



The art of pruning takes into account all these characters in 

 each individual tree in relation to the conditions both below 

 ground and above ground in which it grows, and I say without 

 (jualification that the trees in the Mall are a picture of the 

 correct art of pruning in relation to environment. 



