The Diameter-Increment of Trees.' 
BY 
A. W. BORTHWICK, B.Sc. 
There are two methods, apart from the use of callipers, by 
which the diameter-increment or rate of growth in thickness of 
trees can be ascertained. One of these—the tape-method— 
has already been described by Dr. Christison ; the other is by 
use of a very simple instrument invented by Pressler, and 
known as Pressler’s increment-borer. By means of this instru- 
ment cylinders of wood about a quarter-inch in diameter and 
from two to six inches long—according to species—can be 
extracted, and upon these the breadth of the year-rings may be 
measured. In order to allow for any eccentricity or irregularity 
of growth it is safer to take the mean of four cylinders, one from 
each end of two diameters at right angles. 
The great difference between these two methods is that the 
tape-method requires a very considerable period of time in 
order to get reliable results, as we cannot draw an average 
from one or two season’s growths. In very few cases have 
careful measurements extending over a long period of time been 
carried out, but in the whole history of British arboriculture 
there is no place where more extensive and careful girth- 
measurements have been made than in the Royal Botanic 
Garden, Edinburgh.’ 
By the kind permission of the Regius Keeper I have 
the rare opportunity of testing whether the increment-borer 
would yield the same, or approximately the same, results as were 
obtained by Dr. Christison by means of the tape. The trees I 
examined were those measured by Dr. Christison, and the 
' See Notes from the Royal Botanic Garden, Edinburgh, Number III. 
(1900), p. 4 
(Notes, R.B.G., Edin., No, V, rgor. 
