3 T 4 
Whitby . — - Variation in Hevea brasiliensis. 
variation between individual trees, in regard particularly to rubber yield, on 
an area planted, as all the Eastern plantations have been, from non-selected 
seed, and to suggest the extent of possible improvement in the yields of 
plantations which seed selection might bring about. 
Variation in the Rubber Content of Samples of Latex. 
In order to decide as to whether the rubber content of the latex (the 
‘ strength ’ of the latex) was sufficiently constant to make it feasible to 
lighten the burden of collecting yield data from individual trees by 
measuring volumes of latex instead of taking weights of rubber, the 
strength of the latex from a number of individual trees in the population 
was determined. These determinations revealed unexpectedly great 
variations in the strength of the latex from different trees. A frequency 
table for the samples of latex from the 245 trees examined is given in 
Table I. In each case the latex was diluted with an equal volume of water, 
and coagulated with acetic acid ; the coagulum was converted into crepe, 
and the crepe, after being allowed to dry in the air, was weighed. 
It was found that the strength of the latex from a given tree was 
approximately constant on different days, 1 and appeared to be characteristic 
for the individual tree. Several trees were kept under observation for more 
than a year ; and it was found in these cases that, although, as was 
expected, the strength of the latex from a given tree changed to a certain 
extent with the weather, yet a tree yielding at one time latex with a rubber- 
content clearly higher than the average could be relied upon to yield 
strong latex at all times (and vice versa), 2 and that, by taking samples of 
latex from a number of trees over a short period such that weather 
conditions would not be likely to affect the trees to seriously unequal 
extents, a very fair comparison of the trees in respect of this characteristic 
could be made. 
Table I. 
Rubber Content of Latex from 245 Trees of Hevea brasiliensis , Seven 
Years Old. 
Grm. rubber per 
100 c.c. 
us On *-< cc 10 j>. o\ t-t co 10 w c\ m ro in 
<N «M d CO CO COCOCO 
CO | | 1 I I 1 i I I I I I I 1 I I 
<N -rt-vooo O <N Tt-vooo o <M ^t-vooo O <N t*- 
ci <m o cococococo^-' , ^-ri-Tj-Thif5ir5io 
Frequency 
4 2 7 n 16 27 44 35 23 32 17 12 5 1 4 3 
Mean = 36*58 + 0.25 per cent. 3 <r = 5*86 + 0*17 per cent. CV. = 16*02+0*49 per cent. 
2 
1 The trees were tapped once a day only — in the early morning. It was found that when trees 
were tapped in the afternoon as well as in the morning the strength of the latex obtained on the 
second occasion was usually markedly lower than of that obtained on the first. 
2 Cf. Bulletin No. 13, Dept. Agric. Ceylon, 1914. 
3 This figure, it should be noted, refers to seven-year-old trees. The age of a tree is a factor 
in determining the strength of its latex. The author concluded from a limited number of observations, 
concerning areas from four to eighteen years old, that, as a tree grows older, the rubber content of 
the latex yielded by it increases 1-2 per cent, per annum. 
