GIRTH INCREMENT OF HEVEA BRASILIENSIS. 
79 
Hevea hrasiliensis, after attaining the age of two years, 
sheds its leaves completely, once a year, at Peradeniya, and, 
as in the case of most other deciduous trees which have a 
yearly period, this occurs during the dry season. Flowers 
are produced immediately after, or simultaneously with, 
the new leaves (about March- April), and the fruit ripens iti 
August-September. 
From the curves for 1912 it will be seen that there is no 
increase in growth, as a rule, during the dry period, January- 
March, in which the leaf-fall occurs. As far as is indicated 
by external measurements, growth in thickness begins at the 
end of March or the beginning of April, and continues at a fairly 
uniform rate until about October. It then falls off to about 
half its former rate during October, November, December, 
or it may cease altogether at any date during these months. 
It has to be borne in mind that the data here recorded 
were obtained by external measurements, as in the earlier 
experiments on the same subject in temperate climates, and 
they do not necessarily give any indication of the actual 
activity of the cambium at a given date. Brown (1) has 
pointed out that “ any data secured through bark measure- 
ment are unreliable because of the continual changes going on 
in the older parts of the secondary cortex, and changes which 
bear no relation to the newly -forming rings. As a result, only 
broad generalizations can be drawn from data based on such 
methods.” It is probable that such changes are of minor 
importance in the present case, as the trees were young and 
the bark smooth and continuous during the period mider review. 
In Brown’s experiments on Pinus Strobus, based on the 
determination of the actual increment in the annual ring, 
two periods of optimum growth intensity during the year 
were observed. “ The cambium may be very active for a 
time, then slacken its growth, this to be followed again b}^ 
renewed activity, with a final slump toward the end of the 
growing season.” He notes that this had been previously 
determined by Friedrich, who made his observations with 
the help of calipers and found that in both coniferous and 
hard -wood trees there were two periods of growth, one lasting 
to the end of May, then sinking until the middle of June, 
