288 



For that purpose a few trees were, in that year, worked with a 

 larger number of incisions than was the case in the previous year. 



Tree No. 3 yielded, at the first tapping in the first year from a 

 surface of 2'6 M. 2 and a total length of the incisions of 104 cm., 411 

 grammes of rubber. 



At the second tapping in November of the same year, these figures 

 were, respectively, as follows, 2.6 M 2 ; 320 c. m. and 998 grammes: — 

 and at the third tapping in the following year, 3.27 M 2; 740 cm., 

 and 1332 grammes. 



Reducing the yields to M 2 surface, then we get with 104, 320, 

 and 740 cm. lengths of incisions, respectively, 158, 384 and 407 

 grammes. With a proportion of lengths of incisions of 1 : 3 : 7; the 

 ratio of the yield is as 1 : 2: 4: 2*6. 



These last are not in proportion to the number of incisions. The 

 most unfavourable is the case in which the number of incisions is 

 taken 7 times greater. 



The figures are readily comparable, because the tap periods were 

 nearly equally moist, only in the last case it was cut 10 times instead 

 of 11 times, as had been done in the other instances. 



It is a mere chance if the temperature of the one year is the same 

 during tapping season as that of the following year. 



Small variations do not harm, but large differences in the number 

 of rainy days and the quantity of fallen rain influence the yield of 

 rubber to a high degree as we shall be able to point out with figures 

 of our experiments of tapping. 



From the above experiments we see that an increase of the num- 

 ber of incisions furthers the yield of rubber, but not in the same 

 proportion. 



As the incisions always cause more or less harm to the tree, we 

 must not make this number greater than is necessary to get nearly 

 the biggest possible yield. 



According to the above experiments, an increase of 23 grammes 

 of rubber per square metre of tapped surface is only obtained after 

 more than doubling the number of incisions. 



In the second year, the trees were tapped as high as possible, 

 usually to the point where the branches begin to appear. In order 

 to be able to tap at that height, ladders had to be used. 



In tms wa y> however, much time was wasted in the collecting. 

 Vv e then came to the conclusion that it is of no advantage to tap 

 the trees to a height which the native tappers could reach with 

 ease without having to make use of ladders. 



From former experiments made, we knew already that the lower 

 part ot the trunk gave the bigger yield. 



We shall see from experiments of the second and third year that 

 the lower tapping is more advantageous, 



