Broadly there are only two methods employed in obtaining the latex from Hevea Brasiliensis. The first is that employed in South America, where incisions are made by means of a light axe. The other is the system of excision, or paring, of the bark practised on plantations in the East.

In the early days of the plantation industry, the South American method seems to have been employed, and the writer has knowledge of trees on one of our best-known estates in Malaya which still exhibit the outward and visible signs of that method. At a comparatively early stage, however, the method of excision was introduced. Curiously enough there appears to be no record of its inception or of the individual who was responsible for the substitution of this method. We have been so accustomed to regard it as one of the ordinary facts of estate procedure, that this point seems to have escaped notice and enquiry.

As a variant of these two main methods, a slight vogue was for a short while obtained by the operation known as “pricking.” This was generally combined with excision of bark, and was then known as the “paring and pricking” method; but the simple operation of pricking alone had its adherents, and various forms of instruments were designed to achieve the object. As a means for obtaining a flow of latex, pricking may have been effective, but the general difficulties attaching to the collection of the latex was such as to put the method out of favour.

In the employment of “paring and pricking,” a thin shaving of bark was excised on one occasion. At the next tapping no bark was excised, but a pricking instrument was used along the previously cut surface. It was not proved that any advantage was gained by this method, which was more commonly employed in Ceylon than elsewhere, and it would be surprising to find it in use at the present day.

In the ordinary way the method of excision is practised in such a manner that the “cut” gradually descends to the base of the tree.

Planters with original views, and of an enquiring nature, often query the common practice; and it has been suggested that “as the latex descends by the force of gravity,” one’s paring should be done in an upward direction, thus obtaining a greater pressure of latex—and hence a greater flow. It will be obvious that it would be no simple matter to collect effectively the latex thus obtained from the under edge of a sloping cut, but apart from this the argument would appear to be founded upon what is now accepted to be a fallacy—viz., that the latex per se is manufactured in the leaves and gravitates down the tree.Former Systems of Tapping.—To hark back ten years in the plantation rubber industry is equivalent to delving into history, since development has been so rapid. It was then thought necessary to place upon the trees a number of simultaneous cuts which the modern planter would judge to be inconceivably excessive. Were it not for evidence in the shape of photographs extant, it would be difficult to convince a young planter that such systems were employed.

It was not uncommon for trees to have from six to ten cuts, sometimes all placed on one half of the tree in a herring-bone fashion, and sometimes divided into two portions, each of which tapped the opposite quarter panel of the tree’s circumference. Such superimposed cuts were spaced from 1 foot to 18 inches apart.

On other occasions, a spiral cut was employed, commencing at a height of, say, 5 feet, and gradually descending to the cup at the base of the tree.

Later systems varied from several cuts on a half-circumference, or on a quarter of the tree, tapped either daily, or on alternate days, to cases in which one-third or one-fifth of the tree was employed. Also popular were the systems of the V and half-spiral cuts on half the circumference.It did not take long to be recognised that with all these systems demanding a number of simultaneous parings from the same panel of bark, the rate of excision was so heavy that the period available for the renewal of bark was insufficient for continuous tapping.As a result most of the systems specified have fallen into desuetude, and the tendency has since been to reduce the number of cuts, or the periodicity of tapping, so as to allow for increasing periods of bark renewal.

In the earlier days, a period of four years was thought to be an extremely generous allowance, whereas six years is now becoming recognised as a minimum necessity. Eight years is not regarded as extravagant, while with older bark on some estates periods of ten and twelve years have to be allowed for full renewal. Even so no finality has been reached, and no general rule can be laid down. Local conditions of planting and growth exercise great influence, and the writers have in mind instances in which a period of eight years has proved to be insufficient even for a first renewal after the excision of virgin bark.In the main the most popular systems of tapping are:

Variants and extremes are:

Superficially viewed the latter is four times as strenuous as the former, and the relative position seems to be inexplicable. It may be explained that as a rule the former system is practised on old trees with poorly renewed bark, in order to allow for adequate bark renewal; and the latter is employed in opening young trees just brought into tapping, when the rate of bark renewal is at a maximum.

A few estates in this country still continue to tap trees by means of two superimposed cuts on a quarter of the tree. This was a very popular system some four or five years ago, but it has come to be recognised by practical experience that any system employing superimposed cuts leads to a high consumption of bark without proportionate increase in yield. For instance, if one compares the system of two cuts on a quarter tapped daily with a similar system employing only one cut, one finds that the major quantity of latex is yielded by the lower cut, and that the single-cut system which excises approximately half the amount of bark gives about 80 per cent. of the yield obtained by the tapping of two superimposed cuts.

Of experiments to test the relative values of different systems of tapping there have been many. Most of them suffered from the initial handicap that they dealt with systems which were then popular. In order to obtain any valid result they had to be undertaken over a long period. Meantime there was a progressive movement in actual estate practice towards a greater conservatism in bark removal, and hence the experiments as originally planned lost value.

Moreover, in Malaya it was difficult for experimenters to obtain practical support in the form of areas of trees suitable for experiment. As a result experiments were often confined to small blocks of trees, and a small number of blocks, from which any conclusions derived were subject to considerable errors of experiment. Often comparisons were made between only two blocks, and no allowance was made for varying factors, such as initial differences in yielding capacities of the trees, soil conditions, or the personal equation of the tappers. As a general rule, therefore, the results were vitiated to a very appreciable extent.

All these factors were later taken into consideration in an experiment undertaken on behalf of the Rubber Growers’ Association. In this instance unique facilities were provided by the London Asiatic Rubber Company on their property at Semenyih Estate, and it is only fitting that the company should receive the recognition which its enterprise deserves.

It would have been a great advantage to have included in that experiment other features which have since come into prominence, but the original scope of the experiment had to be confined to the point of comparing yields obtained in making comparative tests based on one system of tapping with different frequencies. Such data were required as a check upon a Ceylon tapping experiment which had attracted much attention. In that experiment trees were tapped at intervals ranging from one day to seven days; and it was concluded that after a period of three and a half years trees tapped with greater intervals gave yields equalling or exceeding those obtained from trees tapped with shorter intervals.

In the Semenyih experiment the system chosen was that which had the greatest contemporary vogue—viz., two superimposed cuts on a quarter of the tree. The various blocks were tapped respectively every day, every second day, and every third day.It was found that the conclusions drawn from the Ceylon experiment were not confirmed. After a period of three and a half years’ continuous tapping neither the alternate-day system nor the third-day system gave results in any way approximating to the yield of the daily system.

The actual average yields from these systems over the whole period were in the order of—

and throughout the course of the experiment neither of the other sections showed any appreciable improvement in position relative to the daily section.

In actual yields “per tapping” over the whole period the alternate-day and the third-day divisions showed advantages of 20 and 35 per cent. respectively over the daily portion.At the beginning of the second year of experiment another section of blocks was opened with a single cut on a quarter, tapped daily. This enabled direct comparison between the values of one cut and two cuts on a quarter in daily tappings and between a daily single cut and two cuts tapped alternate daily.It appeared that the daily single cut yielded over the period of experiment 80 per cent. of that obtained by tapping two cuts daily; and that in the comparison between two cuts tapped alternate-daily and a single cut tapped daily the latter had an advantage of about 40 per cent. in yield.

This result has been used by advocates of daily tapping generally, but it does not constitute a fair argument, inasmuch as the single cut was tapped twice as often, and its position was always relatively low on the hole of the tree. It has been shown in the comparison between the daily single cut and the two cuts daily that the influence on yields of the superimposed cut is relatively small. A fairer comparison would have been obtained if the two cuts tapped alternate-daily had been either amalgamated to form one long cut on half the tree or to form a V on half the tree, thus placing the cuts in the opposing sections on the same level. With the knowledge that the yield obtained from cuts is always greater per tapping by using the alternate-daily system, it would appear to be plain that the one long cut on half the tree would at least equal the yield of the single short cut tapped daily on a quarter tree.

Unfortunately no opportunity has been afforded up to the present of definitely proving this point by prolonged experiment under strict conditions. It is true that the view is held strongly in some quarters as a result of the experience of managers, chiefly on their own estates, that alternate-daily tapping generally gives better yields than daily tapping.

In a number of instances this view is probably correct, and the writers are in agreement; but it is necessary to clear away some misconceptions which confuse the issue. In the main there are two schools, one of which plumps for alternate-daily tapping, while the other adheres strongly to daily excision. Great confusion exists, inasmuch as in many instances the disciples of these schools are really discussing different matters. In the case of managers who argue for alternate-daily tapping their experience is gained, with very few exceptions, from systems in which the excision covers half the circumference of the tree; whereas in almost all cases daily tapping is confined to a single cut on a quarter of the girth. Bearing on such a comparison there are, as far as the writers are aware, no reliable published experimental results. To compare the results obtained from one system practised on one estate with the results of the other system established on another estate is not strictly permissible, as we know that conditions generally may vary to an enormous degree.

The controversy has raged, however, to such an extent that many who are not directly engaged in estate practice have obtained confused impressions. For instance, it appears to be the belief in some quarters that alternate-daily tapping, when applied to a single cut on a quarter of the tree, will yield more than an exactly similar cut tapped daily. In support of such a statement there does not appear to be any confirmation under normal conditions; although such a result might be obtained in the case of old trees which have been heavily over-tapped in the past, and on which the rate of bark renewal has been appreciably retarded. It might also be the case eventually when trees with the opposing frequencies have been tapped for a period extending into many years; but it is the opinion of the writers that under normal conditions such a result would be extremely doubtful.When we come, however, to a comparison of daily tapping on a single cut on a quarter with double the length of that cut on half the circumference, at the same height, tapped alternate-daily—whether in the form of one long cut or in the form of a V—we arrive at a contrast which gives a clear issue. As already stated, facts and figures of reliable experiment are wanting; but it is the opinion and experience of the writers that the alternate-daily system at least suffers no disadvantage on the point of yields, and in other respects, such as conservation of labour and costs, is superior to the daily system.