Observations on the Girth-increase of Trees in 
the Royal Botanic Garden, Edinburgh, for 
Twenty Years, 1878-1897. 
BY 
DAVID CHRISTISON, M.D. 
PART I—DECIDUOUS TREES. 
—_—_—_ 
THE late Sir Robert Christison, when nearly four score years 
of age, began in 1875 a series of girth-measurements of trees 
on scientific principles in order to ascertain their annual girth- 
increase, and was, I believe, the first to do so. The observations 
for the first three years were initiatory upon a few trees only, 
but in 1878 systematic observations were begun on a much 
larger number. In a series of papers read to the Botanical 
Society of Edinburgh in 1878, 1879, 1880, and 1881, he explained 
his methods, gave the results of his observations, and showed 
the practical uses to which such observations could be put. One 
of these,—the rather elaborate computation of the age of trees 
from a series of girth-measurements in a particular tree and in 
others of the same species at different sizes,—has been super- 
seded by the process of extracting borings on which the annual 
rings can be counted, and for practical purposes the same ready 
method is applicable in determining the present rate of growth | 
of a stem; but for this purpose it is necessary to take the 
average of sagoel borings in the circumference of the tree, and 
girth-measurements probably yield more precise results in 
dgtermining, not only annual increments, but more particularly 
the finer rates for months or even shorter periods. It must 
always be remembered, however, that such measurements show 
[Notes, R.B G., Edin., No. III, rg00,] ~ 
