Causes of variation in Growth — Overcrowding 69 



the grounds of Mr. A. Dixon at Cherkley Court in 

 the middle of the unrivalled grove of yew-trees which 

 flourishes there. In the same snowstorm some fine 

 trees in the Druids' Grove at Norbury were much 

 injured. In one instance all the upper boughs of a 

 large tree were broken off, while the lower ones 

 were all bent down to the ground, and remained 

 permanently in that position. The trunks of these 

 trees are now densely covered with young spray. 



Overcroivding, as a reason for diminished rate 

 of growth, appears in the investigations of Pro- 

 fessors Hartig and Weber.^ ' In those trees which, 

 owing to close crowding in the forest, have only 

 developed feeble crowns, the annual increment is 

 greatest just beneath the crown, and diminishes 

 regularly downwards ; and in very closely-crowded 

 trees . . . the ordinary mode of ascertaining the 

 age of the tree would yield false results, for the 

 number of annual rings at 3 or 4 feet high is less 

 than the number of the tree's life. The physio- 

 logical meaning of the above is, that the small 

 leaf-area does not supply sufficient food-material 

 to provide for the needs of the whole sheet of 

 cambium, and the upper parts take all that is sent 

 down, leaving none for those below.' In those 

 which have well-developed crowns the rule is 

 exactly converse. ' If such trees as the above are 

 suddenly exposed to full light and air by cutting 



^ 'Das Holz der Rothbucke,' Nature, March 28, 1S89. 



