W.hitby . — Variation in Hevea brasiliensis. 
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Malay States, viz. August-November. The element in the weather which 
most markedly influences the yield is the rainfall, the trees yielding better 
in wet than in dry weather. The daily rainfall on the area during the 
course of the observations was recorded. The monthly totals were : 
Aug., 473 in. (rain on 13 days) ; Sept., 12*83 in. (18 days) ; Oct., 6-7 2 in. 
(17 days); Nov. 9-46 in. (17 days). 
The results obtained for the rubber yield from the trees surveyed are 
summarized in the following frequency table : 
Table II. 
Rubber Yield from Population of 1,011 Seven-year-old Hevea brasiliensis . 
Grm. per diem 0-1.5 2 3 4 5 6 7 S 9 10 n 12 13 14 
Frequency 55 84 101 140 95 104 76 78 42 41 37 34 26 13 
Grm. per diem 15 16 17 iS 19 20 21 22 23 24 25 26 27 and over 1 
Frequency 15 7 11 14 5 4 3 4 4 3 4 2 9 
Mean yield = 7.12 ±0.115 grm. 2 a = 5.425 + 0.08. Mode (by inspection) = 4.0 grm. 
CV. - 76.19 + 1.14 per cent. Coefficient of skewness (on a) - +0.575. 
The results are represented graphically in the following diagram : 
The outstanding feature of the variation in rubber yield among the 
population examined is sufficiently indicated by the high coefficient of 
variability, and the marked positive skewness of the frequency curve, viz. 
the presence of an important number of trees which are yielding amounts 
of rubber several times larger than the modal value. 
1 Mean of this group, 35.74 grm. 
2 Equivalent to 5.49 lb. per tree per annum. Making due allowance for the effect of wintering, 
for the time occupied by the establishment of wound response, &c., this figure accords fairly with the 
vield of 360 lb. per acre per annum which the section of the plantation in question was giving over all. 
Lump rubber, i. e. natural coagulum which forms in the collecting cups, is included in the 
yields recorded, but 1 tree scrap i. e. rubber obtained from the latex which is left on the cuts after 
the trees have ceased to drip, is neglected. The average amount of tree scrap which each tapping 
gives is indicated by the following figures: (a) 195 trees gave 134 grm. tree scrap; (. 6 ) 190 trees 
gave 1I5 grm. tree scrap. 
A a 2 
