INCREMENT OF TREES, 195 
borer—it is extremely interesting to find how closely they 
coincide. The actual figures are not the same, because the 
borings were not taken at the same level as the tape-measure- 
ments. I purposely took them slightly higher or lower as seemed 
expedient in order not to interfere with the marked circumference 
‘measured by Dr. Christison. 
Although the actual figures for each separate year do not 
exactly coincide, still the mean or average increment for a period 
of five or ten years does correspond very closely. In order to 
show the parallelism between both methods 1 have arranged the 
final results in adjacent columns in the appended Table 11. 
It has been suggested that the increment-borer might damage 
the trees, but if care is taken to properly fill up the holes no 
danger can possibly exist. I may also point out that a very 
short time is required for the tree to naturally occlude such a 
trifling wound as the instrument makes. In almost every case 
the trees which I bored in the spring of last year were occluded 
by the autumn of this year and scarcely any trace of a scar 
remains. 
The increment-borer can also be used in pathological work. 
For example, in making artificial infections, in order to study the 
course of development and effect on the tree of any wood- 
destroying fungus, there is no better method than to introduce a 
cylinder bored from a diseased tree into a healthy one. It is 
then an easy matter to extract cylinders from such an artificially 
infected tree at different times and from different parts, and thus 
get exact information regarding the rate at which the disease 
spreads and the various pathological appearances presented by 
the wood as the disease runs its course. 
In determining the age of trees, if the diameter is not more 
than one foot the number of year-rings on an extracted cylinder 
will give this at once. If it is not possible to bore right into the 
centre we can still obtain the number of year rings on a certain 
length of the radius and from this compute the probable amount 
on the whole, always taking care to allow for the greater year- 
ring breadth near the centre of the stem. In many cases the 
pith is eccentric ; if, therefore, we bore four cylinders in the radial 
direction one of them is generally found to reach the pith even 
though the diameter of the stem be more than one foot, 
