516 
Philippine Journal of Science 
1919 
It is recognized that the results are subject to criticism from 
a scientific viewpoint, but it is believed definite data in regard 
to the girth of Hevea brasiliensis in the Philippine Islands are 
of sufficient practical importance to warrant their publication. 
It would undoubtedly have been desirable to remeasure the same 
trees through several successive years; but, since this has not 
been practicable, the results of the present series are given in the 
table to show the growth attained by trees at certain known 
ages. An attempt has been made, by averaging a number of 
measurements, to neutralize individual variation among trees of 
the same age as such variation in Hevea is well known to be 
considerable. Under apparently identical conditions certain in- 
dividuals may attain as great a girth in five years as others do 
in seven or eight years. 
Conditions of cultivation are approximately equal for all the 
trees considered. A strip about 3 meters wide is kept clean- 
weeded along the rows, and the remainder plowed about three 
times each year. The older trees were planted at various dis- 
tances, but later plantings are all 5.49 by 5.49 meters (18 by 18 
feet). In each case the planting distance is indicated. In the 
older blocks the retarding effect of close planting on the growth 
of the trees is very evident. The trees have practically ail been 
tapped since they attained a diameter of 50.8 centimeters (20 
inches) at 45.7 centimeters (18 inches) above the ground. 
MEASUREMENTS OF TREES ON BASILAN ISLAND 
In Table X the measurements of five hundred fifty-one trees 
of various ages are given. The age in months of each group is 
recorded, together with the planting distance and general char- 
acter of the land. Measurements were made with a tape to the 
nearest 5 millimeters at 1 meter above the ground. For each 
group the maximum, minimum, and average girths are indicated. 
A certain error is caused by the fact that the measurements were 
necessarily made over the tapping surface, but this error is prob- 
ably never very great and is in the direction of a reduction 
rather than an increase in the recorded girth of trees at the 
various ages. Most of the measurements of trees in other coun- 
tries with which the Philippine trees are compared have been 
measured at 1 yard from the ground; and, since the trunks of 
Hevea brasiliensis taper rather abruptly, this difference in height 
of measurement has the result of reducing the girth of the 
Philippine trees when compared with others. This comparative 
reduction ranges from a few millimeters for the younger trees 
up to approximately 1 centimeter for trees 10 years of age. It 
