Variation in Hevea brasiliensis. 
BY 
, STAFFORD WHITBY, M.Sc., A.R.C.S., 
McGill University , Canada. 
With one Diagram in the Text. 
I T was desired to secure data as to the extent to which variation occurs 
in the amount of rubber yielded by individual trees of Hevea brasiliensis , 
of the same age and growing under the same conditions, and as to the 
possible correlation between the yield of rubber and the girth of the trunk. 
In addition to data directly relative to the matter just mentioned, the 
observations which have been made afford information concerning the 
extent of variation in the rubber content of the latex from individual trees 
and concerning a number of other points noticed in what follows. 
The observations were made in the Federated Malay States. A normal 
area of plantation rubber trees, 7 years old, was selected. The area was 
approximately 13 acres in extent and contained 1,338 trees, planted 20 feet 
square. Of these trees 1,137 were in tapping. The trees comprising the 
balance of 201, not in tapping, were mostly ‘ supplies i. e. trees which had 
been put in since the area was first planted up in order to fill vacancies 
caused by disease, pests, wind, &c. These trees were of course younger 
than the other trees on the area and, owing to overshadowing, had not had 
a good chance to grow. They were, in fact, all removed in the ordinary 
course of thinning-out operations on the plantation in question soon after 
the close of the observations recorded here. Of the 1,137 trees in tapping, 
106 were one year behind the remainder in their tapping history ; having 
attained a trunk-girth up to the standard fixed for the commencement of 
tapping operations about one year later than the rest of the trees. Some 
of them doubtless represented the original plantings, but others no doubt 
represented ‘ supplies ’. As no means were available for distinguishing 
original plantings in this group from c supplies \ and as these trees were 
being tapped at a lower point on the trunk than the rest, they are not 
included in the present survey. Of the remainder of 1,03 1 trees, 20 are not 
included because of incompleteness of the record or failure of the tappers to 
cut deep enough. The data refer, therefore, to a population of 1,01 1 trees, 
in their third year of tapping, on a normal plantation area of seven-year- 
old Para rubber. They serve sufficiently well to indicate the extent of 
[Annals of Botany, Vol. XXXHI. No. CXXXI. July, 1919.] > 
