and Magazine of the Ceylon Agricultural Society.— October, 1912. 333 



HEVEA RUBBER EXPERIMENTS AT 

 HENERATGOBA. 



BULLETIN BY R. H. LOCK, ScD., F.L.S. 



AND M. K. BAMBEK, F.I.C., M.E.A.C. 



The first bulletin issued under the auspices 

 of the newly formed Department of Agriculture, 

 is devoted to the Heneratgoda Experiments for 

 1911-1912 and has been prepared by Dr. R. H. 

 Lock and Mr. M. Kelway Bamber, who have 

 been in charge of them. Two other bulletins, 

 dealing with the subject have been issued 

 already and the present forms part third 

 of the series. The present circular covers the 

 ground for 1911 and the first four months ot 

 1912. The experiment is still a long way from 

 completion and the present communication is 

 to be regarded only as an interim report. The 

 experiment consists in the tapping of seven 

 rows of ten trees each, all being treated 

 alike, except that each row is to be 

 tapped at a different interval of time. 

 The trees used in the experiment were ap- 

 proximately twenty-five years of age, and had 

 not been tapped previously for some years. 

 A table giving the average circumference of each 

 set of ten trees in June 1908 and June 1912 

 shews only a email increase in girth, ranging from 

 an average of '65 inches to an average of l - 48, 

 which is put down by Dr. Lock and Mr Bam- 

 ber to close planting. The system of 

 tapping was as follows : — The bark to a 

 height of six feet was divided into four equal 

 areas, each extending half way round the tree. 

 Each area was occupied by three V-shaped cuts. 

 The four areas were tapped in succession — first 

 the lower half of one side, then the lower half 

 of the other side, followed by the twoj upper 

 areas in the same order. The tapping was not 

 very successful and on June 8, 1911. an important 

 change was made in the method. Before this 

 date the trees were pared with the Bowman- 

 Northway knife and immediately pricked with 

 the sharp pointed spear pricker. From June 8th 

 onwards the paring knife was used alone, with- 

 out the pricker, the paring cut being made 

 slightly deeper. All the experiments, we are 

 told, made botn at Peradeniya and Heneratgoda, 

 point to the superiority of the method of paring 

 over that of combined paring and pricking, In 

 fact several trees of the present experiment 

 were showing signs of injury which are 

 believed to have been occasioned partly by the 

 method employed. 



The new method of paring only was followed 

 by a marked increase in yield towards the end 

 of 1911, but probably only a small part of tbe 



increase can be attributed to the new way of 

 releasing the latex. On the other hand, the 

 usual seasonal increase was emphasized in 1911 

 by the fact that the climatic conditions were 

 exceptionally unfavourable for a good yield 

 during the first half of the year, and, during the 

 second half, unusually propitious. In addition 

 to this, Dr, Lock and Mr. Bamber have every 

 reason to believe that the stimulus of three 

 years' tapping had by this time led to the pro- 

 duction of new layers of laticiferous bark, pos- 

 sessing a markedly enhanced capacity for latex 

 formation. This view, derived from a compari- 

 son of the yields of the different rows at diffe- 

 rent seasons and stages of tapping, is confirmed 

 by the yields obtained from the renewed bark 

 of the old tree. 



As in previous Circulars, the results of the 

 experiments are set forth in a series of tables. 

 The annual yield varies from 1*2 lb., with 

 tapping at an interval of 9 days, to 2'85 lb, 

 with tapping at an interval of 1*4 day. These 

 yields are, we agree with Dr. Lock and Mr, 

 Bamber, extremely small for such old trees. 

 A table giving the average yields per tapping 

 in 1909-1911 shows that on the average the yield 

 per tapping is lowest in April and May. The 

 yield rises continuously until December and 

 then steadily falls off again. The increase from 

 April to December on the average of these 

 three years, and taking the average result of 

 various intervals of tapping, does not fall far 

 short of 50 per cent. 



The percentage of rubber in the latex, from 

 month to month, is shown in tabular form. 

 The only new fact of special interest which 

 presents itself in this connection is the marked 

 increase in the percentage shown by all the rows 

 of trees at the beginning of 1912. Dr. Lock and 

 Mr. Bamber think it will be convenient to post- 

 pone the further discussion of this phenomenon 

 until further data are available. The most 

 important new fact which has come to light 

 during the past year of tapping lies in the 

 increased yields obtained from the later tapping 

 of the rows tapped at longer intervals. 



On the subject of overtappiog the bulletin has 

 something interesting to say. 



A strictly satisfactory definition of overlap- 

 ping, it seems, has still to be devised. The pro- 

 blem has been, however, brought so prominently 

 before Dr. Lock and Mr. Bamber by the facts 

 recorded in the present bulletin, that it seems 

 desirable to them to attempt a preliminary dis- 

 cussion of overtapping which may lead to a 

 partial elucidation of the subject. Overtapping, 

 tbey Bay, may be measured either by removal 



