It is possible that the immediate response to tapping is partly due to a reduction in the viscosity of the latex, which is thus enabled to flow more freely. When part of the latex is removed from the vessels by tapping, the internal pressure of the latter is reduced and the remaining latex is diluted by the entrance of sap from the surrounding cells. The pressure in the surrounding cells may also be increased owing to the irritation consequent upon wounding. It is a fact that the proportion of caoutchouc in the latex often falls off rapidly during the first few tappings. The important point to be observed, however, is that the yield shows no diminution for a considerable period in spite of continued tapping even at daily intervals. Table XI shows the yields of dry rubber from 70 trees tapped at Henaratgoda. beginning in June 1908.

The trees were taken in groups of ten, numbered from I to VII respectively, and the average interval in days between successive tappings in the case of each group was as follows:

Table X. Average Intervals Between Tappings

The interval aimed at was an even number of days in each case. The actual excess was due to the fact that it was not always found possible to tap on the appointed day.

The tappings at longer intervals extended of course over a longer period of time than those at shorter intervals, consequently the climatic conditions are not identical in the case of the results recorded in different columns of Table XI. Nevertheless it will be observed that the variations in yield throughout the whole experiment were comparatively small.

In other experiments a larger initial increase in yield was observed. In such cases the results resemble those of Parkin more closely. It must be remembered also that the method of tapping employed was entirely different from that of Parkin, who used an incision method pure and simple, and did not reopen the same wounds. The result of all such experiments may be summarised as follows. With any moderate method of tapping, carried out at nearly equal intervals, which may vary in length from 24 hours up to 10 days, the yield per tapping rises rapidly to a point at which it is subsequently maintained, subject to certain variations the nature of which will be considered later on.

Table XI. First 40 Tappings

Total Rubber from 10 Trees tapped at intervals of 1—7 Days (nominal). (Weights in grammes; circumference in inches.)

1 An interval of 11 days between the *8th and 19th tapping of row I., and between the 14th and 15th tapping of row II.