3i5 
Whitby . — Variation in Hevea brasiliensis . 
The samples of latex included in the table were taken mostly from 
the larger yielding trees (mean yield n*8 grm. per diem). The figures did 
not, however, indicate that there was any correlation between yield and 
latex strength. The figures may thus be considered as fairly indicative of 
the whole population in regard to the strength of the latex. 
Variation in Yictd. 
The exact magnitude of the yield of rubber given by any one tree 
varied at different times, but was found to be, in general, sufficiently 
constant to allow of a fair comparison of the yielding capacities of the trees 
on a given area under similar tapping conditions being made by taking the 
mean of the yields on a number (in these observations, mostly six, but in 
some cases ten to twelve) of separate days. 
It seemed clear that, although the actual magnitude of the yield from 
a given tree varied to a certain extent at different times, owing to variations 
in fortuitous circumstances, such as the rainfall, the prevailing humidity, 
the depth of tapping, the hour at which tapping is performed, yet trees 
presented characteristic differences in their capacity for yielding rubber, 
and, at all events in a first investigation, might reasonably b® compared in 
respect of this capacity by taking measurements under conditions such that 
variations in the fortuitous factors which influence the yield were as far as 
possible avoided, or affected all trees equally, and by, in addition, basing 
conclusions for any given tree on the mean of several determinations. 
In addition to the evidence as to the comparative constancy of the 
yield from individual trees, which the considerable body of data summarized 
below afforded when examined in detail, further evidence in support of this 
conclusion was secured by keeping a limited number of trees under obser- 
vation for a longer period than that covered by the main series of measure- 
ments. In the case of some of these trees the yield was determined at 
intervals over a period of two years. It was clear that, although seasonal 
variations in the yield took place, the yield for a given tree was in most 
cases approximately constant over such a period. Speaking generally, 
a tree which was seen to be a high yielder at one time could be relied upon 
to give a high yield at all times. 1 
Concerning the factors which, apart from the characteristic yielding 
capacity, affect the yield, the following points are noted : 
(a) All trees were under the same tapping system (a single V-cut on 
1 This conclusion may be considered as being in agreement with general plantation experience. 
Trees are sometimes noted as falling off seriously in their yield or even as * going dry \ (It is pos- 
sible that such behaviour may be due to disease or other abnormal conditions.) But, in general, it is 
recognized that high yielding trees (which naturally come under notice more frequently than other 
trees) can be expected, if not over-tapped, to give high yields during the whole of their tapping history. 
Also cf. the records for the original generation of trees raised from the seeds first introduced into 
the East from Brazil : Bulletins Nos. 4 and 13, Dept. Agric. Ceylon. 
A a 
