The seasonal variation in yield is clearly associated to some extent with the climatic conditions at different seasons, as may be seen on comparing it with the following table which shows the average monthly rainfall at Henaratgoda for the three years 19091911.

Table XV. Rainfall At Henaratgoda, Averages 19091911

Month

Rainy days

Rainfall

(inches)

Month

Rainy days

Rainfall

(inches)

January

4

1.54

July

10

8.88

February

1

.61

August

9

7.04

March

6

3.95

September

5

2.91

April

6

4.43

October

16

24.86

May

10

6.69

November

16

11.81

June

12

9.01

December

9

7.99

It will be observed, on comparing Tables XIV and XV, that the season of highest yield follows shortly after the season of greatest rainfall. In countries subject to a prolonged dry season the variations in yield are much more marked. The following table shows the monthly crops of dry rubber harvested during 1912 on a well-known property in South India.

Table XVI. Stagbrook Rubber Co. Crop Of Dry Rubber In Lbs

Month

Crop

Month

Crop

January

2345

July

2256

February

nil

August

2809

March

nil

September

5871

April

nil

October

9087

May

1205

November

14088

June

2514

December

18000

More than half the total crop was harvested in the last two months of the year.

Some relation can also be traced between the yield and the rainfall at different seasons in any given year. It seems clear however that the variation at Henaratgoda is also affected by other factors. The highest yields are obtained in November, December and January, just before the time of leaf fall. There is then a rapid falling off, and the yield remains low until August, that is to say during the whole time of the formation and ripening of the fruits. This is what would naturally be expected on general principles, although the differences are perhaps less marked than we might have been led to anticipate. Whatever the function of rubber may be, there can be no doubt that its formation constitutes a tax on the food supplies of the tree, whilst the latex removed in tapping contains other materials of possible nutritive value. We should expect the available supplies of food material to be greatest just before, the fall of the leaves, since these are engaged up to the last in food production, and give up part of their organic contents to the tree before they drop to the ground. In April and May, on the other hand, the formation of fresh leaves, flowers and fruits has successively drained the resources of the tree, so that these must be at a comparatively low ebb. We find, accordingly, that the percentage of caoutchouc is highest in December and January, and lowest in May and June.