118 



PROPERTIES OF WOOD. 



HEIGHT -GROWTH continued. 



[This list differs from that given by Mayr, so as to include 

 the economic trees and shrubs that are grown in the British 

 Isles. Under favourable conditions certain trees may pass into 

 a higher height-class. Tr.] 



The development of a tree in height depends on several 

 factors ; for instance, soil, climate and exposure to wind, 

 method of production as well as species. The current height- 

 increment attains its maximum in the pole-stage, then sinks 

 again till maturity is reached, becoming nil in trees with 

 eventually flat or round crowns, such as Scots pine, silver-fir, 

 or cedar, or in trees such as ash and horse-chestnut, where 

 the terminal shoot blossoms. Generally the height-growth is 

 maintained longest when trees are in their optimum climate, 

 on the most suitable soil, and grown in dense but not in the 

 densest crops. It has often been asserted that density 

 of growth favours height in trees, and certainly this is true in 

 the younger stages of growth, just as removal of side-branches 

 in fruit-tree culture favours the leading shoot of a tree. In a 

 group of trees of the same age, the border trees are shortest, 

 and those in the centre tallest. 



Diameter-growth at first falls behind height-growth, 

 especially in dense crops, attains its maximum somewhat 

 later and ends with the deatli of a tree, for every tree 

 forms an annual ring as long as it is alive. Only in very 

 suppressed individual trees, a cessation of diameter-growth is 

 alleged for the lower part of the stem ; this has not yet been 

 proved. Diameter-growth is favoured by the admission of heat 

 and light and the consequently increased nutriment available. 



