Gums, Resins, 



4 



[January, 1912. 



the author himself should these lines 

 happen to fall into his hands. 



Although we agree with Mr. Braham 

 in advocating a comparatively wide 

 distance of planting, we do not know 

 of any direct evidence to show that a 

 wider distance than 15 x 20 feet actually 

 results in a heavier permanent yield 

 per acre, whilst at a greater distance 

 than this initial yields must be materi- 

 ally reduced, and the cost of clean 

 weeding — a process which the author 

 emphasises as essential, becomes practic- 

 ally prohibitive. 



From the statements on pages 26 and 

 27 it is to be inferred that in the author's 

 opinion thumb-nail pruning leads to 

 reduced danger of damage from wind. 

 This is certainly not the general experi- 

 ence in Ceylon, where the practice of 

 topping the trees has been generally 

 given up owing to the injury done by 

 wind to trees so treated. Nor do we 

 clearly understand why a tree which 

 divides into three branches should make 

 less of a cup to collect water, than one 

 which only forks into two. 



It would scarcely be possible for any- 

 one who is familiar with the growth of 

 Hevea and Ceara rubbers to recommend 

 the planting of the latter as a protective 

 belt between fields of the former, 



The author repeats the dictum, due 

 originally, we believe, to Mr. Herbert 

 Wright, that the objective of scientific 

 tapping is to obtain the greatest amount 

 of latex with the minimum of bark 

 removal. If this is the case a method of 

 pricking by which a great deal of latex 

 can be obtained without any removal 

 of bark should be superior to any 

 system of paring. Mr. Braham, how- 

 ever, makes no mention at all of pricking, 

 nor, so far as we can discover, does he 

 ever make use of the word paring, but 

 uses the expression tapping as synony- 

 mous with paring. In a book intended 

 for use on the estate it is also surprising 

 to find no practical instructions for 

 carrying out the actual process of 

 paring, which is much the most difficult 

 and delicate of all the operations con- 

 nected with rubber planting. 



In his explanation of " wound res- 

 ponse " by the sudden formation of 

 new latex vessels in the neighbourhood 

 of the incisions, the author repeats an 

 ancient error. We imagine he can 

 scarcely be aware of the rapidity with 

 which the increased flow of latex comes 

 into operation. 



The third section of the book contains 

 hints for health in the tropics. From 

 the list of the principal diseases to be 

 guarded against en trie fever is omitted. 



R. H. L. 



GUMS, RESINS, SAPS AND EXUDATIONS. 



THE FUNCTION OF CAOUTCHOUC 

 IN THE LaTEX. 



By Dr, H. P. Stevens. 

 Up to the present time there is little 

 or no evidence as to the part played by 

 the latex in the economy of the plant 

 such as can be interpreted decisively in 

 favour of any of the theories that have 

 been enunciated. This applies whether 

 we consider the function of the latex 

 in regard to one species only or to 

 latex-yielding plants collectively, and 

 whether the latex contains an appreci- 

 able proportion of caoutchouc or con- 

 sists almost entirely of ' resinous ' 

 matter. It has been pointed out that all 

 latices do not necessarily have the same 

 functions, but an hypothesis applicable 

 in general to them all should carry more 

 weight than one which can only be 

 applied in individual cases. All latices 

 consist of a watery liquid in which is 

 dissolved practically all the food consti- 

 tuents necessary to plant life, namely, 

 nitrogenous matter, potash salts, phos- 

 phoric acid and carbohydrates. Accom- 



panying these we have a large propor- 

 tion, up to 50 %, of chemically very inert 

 material consisting of caoutchouc and 

 resinous matter, these two in the most 

 varied proportions. Any theory which 

 accounts for the presence of caoutchouc 

 in some latices but does not account for 

 the resins in others is incomplete, and 

 consequently defective, unless some 

 special reason for the different beha- 

 viour of the resins from the caoutchouc 

 can also be formulated. A theory, to be 

 acceptable, should apply to both types 

 of the inert material, that is, both to 

 the caoutchouc and the resin. Thus, for 

 instance, take the negative results in 

 the search for an enzyme or bacterium 

 which would resolve and convert the 

 non-soluble caoutchouc into soluble and 

 assimilable carbohydrates. Were such 

 an enzyme discovered it would be prima 

 facie evidence in favour of the reserve 

 food theory, but the evidence would be 

 incomplete without some satisfactory 

 theory to account for the presence of 

 resins— practically to the exclusion of 

 caoutchouc— in other latices. In paren- 



