Reviews. 



262 



[September, 19il. 



Whilst welcoming the innovation, we 

 are inclined to fear that its teaching will 

 prove ineffective with one class of 

 readers, whereas for another class it is 

 surely superfluous. It is superfluous for 

 those rare individuals who possess the 

 instinct and training npcessary for ex- 

 perimental work ; and we greatly doubt 

 whether the mere perusal of such a 

 chapter will be sufficient to induce scien- 

 tific habits of thought in a mind which 

 is unaccustomed to them. It is true 

 enough that the number of people 

 engaged in experimental work in tropical 

 agriculture greatly exceeds the number 

 of those who are competent to under- 

 take such work ; and the kind of work 

 frequently published calls for all the 

 author's strictures. But it is very 

 doubtful whether the delinquents will 

 ever mend their manners or come to 

 publish useful results. 



It appears, however, that Mr. Fetch's 

 main object in writing this chapter was 

 to educate the critical faculty of the 

 public which reads the published ac- 

 counts of agricultural experiments. In 

 this enterprise we wish him every 

 success, and we hasten to add that we 

 are in hearty agreement with the major- 

 ity of his contentions. 



There is one point, however, closely 

 connected with the art of experiment in 

 which we cannot entirely exonerate Mr. 

 Petch himself from blame. This is in 

 the matter of premature discussion of 

 incomplete results. Mr, Petch has 

 devoted a good deal of space to the con- 

 sideration of figures published by Mr. 

 Kelway Bamber and the reviewer in 

 September, 1910. These figures repre- 

 sented the progress during the first 

 eighteen months of tapping experiments 

 begun in June, 1908. An interim report 

 dealing with the further progress of 

 these experiments was published in 

 June, 1911, but they are still far from 

 complete. In the first of these reports 

 which was the only one in Mr Petch's 

 hands at the time of writing, the authors 

 deliberately reserved their own discus- 

 sion owing to the insufficiency of data. 

 In fact the appearance of these reports 

 was not due to any desire on the part 

 of the authors to rush prematurely into 

 print, but to the exigencies of the public 

 service which demand not only that the 

 tale of bricks should be accomplished, 

 but that this should be accomplished by 

 a suitable display of printed results. 



Thus Mr. Petch devotes four pages 

 (pp. 28 — 32) to a full discussion of the re- 

 lation of the interval between successive 

 tappings to the question of so-called 

 wound response, based upon figures 

 published in the reviewer's first report. 



In his second report the reviewer has 

 pointed out a fact which renders the 

 figures entirely misleading from this 

 point of view. The yields from in- 

 dividual trees also lead to a different 

 conclusion from the one naturally drawn 

 when the trees are taken in groups. 



We may add that we have on one 

 occasion found just as much (or as little) 

 wound response on passing to a fresh area 

 of bark as at the first tapping of the tree. 

 We would point out, however, a circum- 

 stance which does not appear to have 

 occurred to anyone in the course of 

 these discussions, namely, that the 

 opening cut cannot be regarded as in 

 any way comparable with the sub- 

 sequent paring cuts. The opening cut, 

 for example, draws latex from its upper 

 as well as from its lower side. 



On pages 38 and 39 Mr. Petch calculates 

 from our figures that ten trees tapped 

 440 times in a year and a half yielded 

 about as much rubber as their bark 

 could be supposed to contain at the 

 beginning of the experiment. If we 

 apply the same calculation to the best 

 yielding specimen among the Henarat- 

 aoda trees now being tapped, but 

 doubling the postulated thickness of 

 laticiferous bark, we find that this tree 

 yielded in a little over two years five 

 times the amount of rubber present at 

 the beginning of the tapping period. 

 The reviewer's own calculation contained 

 i n Circular No. 20 published in June, 1911, 

 in collaboration with Mr. Kelway 

 Bamber, is based upon a much more 

 liberal estimate of the capacity of 

 the laticiferous system. Whichever 

 estimate is adopted, however, we seem 

 to be driven inevitably to the conclusion 

 that rubber is formed afresh in the latex 

 tubes during the process of tapping— 

 that the tree does in fact acquire or 

 possess the faculty of manufacturing 

 rubber in the old latex tubes — a con- 

 clusion which Mr. Petch appears to 

 adopt with considerable hesitation. 



As regards tapping systems Mr. Petch 

 favours the half-herring bone on 

 successive quarters of the tree, first 

 recommended we understand by Ridley. 

 This is probably the system now most 

 commonly in use. The author is how- 

 ever strongly impressed with the 

 necessity for resting periods in addition, 

 and believes that "Even on the one 

 quarter year system the tree cannot be 

 expected to survive many four year 

 periods if one follows the other im- 

 mediately." This is a question upon 

 which we should hesitate to give a de- 

 finite opinion without further evidence, 

 but there can be no donbt that it is best 

 to be upon the safe side. 



