56 
Indian Forest Records. 
[VOL. VIII. 
No. 2*. Taking the data of this bulletin as a standard the following 
operations are carried out:— r(l) the girth of the mean tree in a plantation 
of known age is ascertained from the curve in Diagram III, (2) the 
number of beeholes occurring in a tree of this girth is read off the girth- 
beehole incidence curve for the plantation, and (3) this value is then 
plotted against the age of the plantation. A curve drawn through 
these points will give the Age-Beehole Incidence. 
In the following records the index of attack for a sample plot is usually 
expressed in the terms of Leete’s normal tree, but in some cases the quality 
growth of the area sampled departs considerably from this mean. It has 
therefore been necessary in these cases to make an arbitrary selection of a 
mean sample tree on which to base the index of attack. The position 
of the arithmetic mean sample tree value with reference to the girth- 
beehoie curve has been used as the principal check. If an extensive 
enumeration of the stand, in which the sample plot is situated, is carried 
out, it is preferable to use the mean sample tree arising from these 
measurements, in place of the data available in Forest Bulletin 2. 
Annual Incidence. 
[Vide Diagram 2.] 
The annual incidence of the plot is obtained by adding together the 
data of all trees in which every beehole can be accurately dated. If 
one or more of the beeholes cannot be satisfactorily dated it is advisable 
to reject the whole tree from the annual incidence figures. The annual 
totals so obtained are then proportionately reduced to the quantities for 
the mean tree ; that is, the sum of the annual attacks on the mean 
tree is equal to the index of attack, i.e., its girth-beehole value. These 
quantities are termed in the Tables of Annual Incidence that follow, 
the Reduced Values. In the Annual Incidence Graphs in Diagram 2 
considerable fluctuation occurs in the current annual incidence, but the 
mean annual incidence on the whole steadily increases, though rela¬ 
tively slowly. It is probable that the apparent variation in the annual 
incidence is due more to the magnification of localised variations (owing 
to the small number of sample trees) than to other causes. The mean 
annual incidence is a truer indicator of local incidence. 
*“ Memorandum on Teak Plantations in Burma,” F. A. Leete, Forest Bulletin, 
No. 2, 1911. 
[ 284 ] 
