196 BORTHWICK—THE DIAMETER- 
The relation between the wood-mass of a tree and the time 
taken to produce it is a subject of considerable scientific and 
practical importance, No matter whether the trees are grown 
for ornamental or economic purposes, a knowledge of the relation 
between time-increment and volume-increment cannot fail to be of 
great service. The proprietor of parks and ornamental policy- 
grounds is always interested to know how his trees are doing, 
whether they are still increasing by growth or are already mature. 
On the other hand in economic forestry it is essential to know the 
amount of timber which is or can be produced in a given time 
under certain climatic conditions and sylvicultural treatment, 
otherwise financial calculations cannot be made with anything 
like the degree of accuracy which the case demands. The 
manifold external conditions influencing the growth of trees and 
plants in general make it well-nigh impossible to lay down any 
definite rules which are generally applicable for all species. A 
tree which is a fast grower in one locality may behave very 
differently in another, hence it is necessary for accurate results to 
collect statistics for each locality. 
At present the German yield-tables are used in this country, 
and for general purposes are found to be approximately accurate, 
but the mere fact that in Germany local yield-tables are found 
to be necessary shows that the general yield-tables are not 
indiscriminately applicable. Our climate being an insular one, 
milder and moister, is bound to have a different effect on tree- 
growth from the continental climate of Europe. 
If statistics were collected, especially for the Highlands, to which 
the German yield-tables are probably least applicable, they would 
be of great service to the forester, especially in making out 
working plans to guide the future management of the forests. 
[ TABLE. 
