The increase in flow associated with wound response is accompanied by a reduction in the concentration of the latex. Hence in terms of latex the increases in yield during the early stages of tapping would be larger than those shown in the various tables in the present chapter, which refer to yields of dry rubber. Table XXI illustrates this fact. This table is the counterpart of Table XI, except that the entries refer to percentages of rubber in the latex, instead of to weights of dry rubber. Table XXI further shows that the falling off in concentration is much more rapid when the tapping intervals are small than when they are larger. After a certain period, which is longer when the intervals are longer, a more or less permanent concentration is reached, which persists for an indefinite period, but is also subject, as in the case of the yield of dry rubber, to seasonal variation. This more or less permanent concentration is considerably higher in the case of the trees tapped at longer intervals.

Table XXI. First 40 Tappings. Percentage Of Rubber In Latex

Average of 10 Trees in each case tapped at intervals of 1—7 Days.

Thus the averages of all the concentrations determined during this experiment, from 1908 to 1911, were as follows:

Table XXII. Percentages Of Rubber In Latex

The seasonal variation in the concentration of the latex during prolonged tapping are similar to those observed in the total yield of dry rubber. The percentage of rubber was found to be generally highest about January and lowest about June. This fact supports the view that the yield depends upon nutrition as well as upon the supply of moisture, since otherwise the concentration might be expected to be highest in the dry season and lowest in the wet. There is however no evidence of an increase in concentration during dry weather.

Table XXIII. Percentages Of Rubber. Monthly Averages, 1909—1911

The concentrations here recorded were determined by dividing the weight of dry rubber by the volume of the latex, a method which gives values slightly too low throughout.

The dry rubber obtained in this experiment from the second to the sixth tapping of each group (samples A), and again after tapping had been in progress for four months (samples B) was analysed for ash, resin and organic matter. As regards ash, practically no difference was found between the product of earlier and later tappings. The proportion of resin showed a slight falling off in the product of the later tappings, especially in the case of the more frequent intervals.

The organic matter in the two series showed differences of considerable interest. In the groups tapped at shorter intervals the organic matter from the later tappings showed a distinct increase, whilst in the groups tapped at longer intervals the reverse was the case. The following purely tentative explanation was put forward to explain these differences. " If we suppose that some part of this organic matter represents the raw material from which the rubber is formed, then, in the case of daily tapping we may suppose that the drain upon the resources of the tree is at first greater than it can cope with, but that later the bark reacts more perfectly to the stimulus of tapping, and produces the raw material faster than the cells can convert it into caoutchouc. In the case of tapping at longer intervals, on the other hand, we may suppose that the stimulus to manufacture rubber leads to an accumulation of this material in the latex tubes, which is only partly removed by the e.g. weekly opening of the vessels, and that this concentration...inhibits the further production of raw material. In other words, tapping stimulates the tree both to the production of the raw materials for rubber and to the conversion of these into rubber. With frequent tapping the raw materials are produced faster than they can be converted; with less frequent tapping the reverse is the case1." It is scarcely necessary to point out that the whole subject requires further investigation from the chemical standpoint. The actual figures obtained in the analyses are given in Table XXIV.

Table XXIV. Analyses Of Rubber From Earlier Tappings

Analyses Of Rubber From Later Tappings