brasiliens is and its Protective Function. 
2 5 l 
above may be attacked by borers and fungi, but that the susceptibility to 
attack is enormously increased if the cork-cambium is removed. The 
scraping of the bark so as to leave the cork-cambium intact, without exposing 
the outer cortical tissues, is a practical impossibility under estate conditions. 
This layer is very thin, and as the scraping would have to be performed by 
coolies, there is not the slightest doubt that large patches of the cork-forming 
layer Vould be removed. Such trees are comparable to the heavily scraped 
trees in the experiment. 
It follows that bark-scraping of any description should be carried out 
with discretion. It is quite easy, with a little care, to scrape off the scaly 
bark on old trees without injury. This is done on large numbers of estates 
to ensure a clean yield of latex. It has been noticed on several estates that 
this has been undertaken so carelessly as to expose the outer cortical tissues, 
thereby laying the trees open to injury. Such carelessness must be severely 
condemned, and estates managers would be well repaid if they inspected 
scraped trees immediately after the scraping. 
To all patent methods of increasing yield of latex there are serious 
objections. It is admitted by authorities that it is possible to exhaust 
a rubber tree by draining it too rapidly of its latex. This conclusion has 
been reached as a result of practical experience. Unfortunately there is 
little positive knowledge as to the function of latex in the economy of the 
tree, and until we gain more knowledge it is necessary to urge the desira¬ 
bility of a conservative attitude in connexion with methods for artificially 
increasing yield of latex. The problem to be solved is whether latex is 
a secondary waste product, the withdrawal of which from the laticiferous 
cells does not influence the vital processes, or whether it is a primary 
product, the withdrawal of which means increased activity on the part of the 
tree, in order to immediately replace that taken away. If the latter, then 
artificial methods of increasing yield beyond certain limits prejudices the 
health of the tree, while if it is waste material, any method of increasing 
yield might be employed, if the method of extraction, i. e. bark removal, &c., 
did not interfere with the normal processes. In estate practice rapid 
removal of bark, which implies insufficient time for a good renewal, is the 
limiting factor in the tapping process, not the quantity of latex extracted. 
The problem stated above is of prime importance for the future of the 
rubber industry. The investigation of physiological problems has been 
neglected in the past, partly because of the difficulties which surround 
investigations of this description in tropical countries, and partly because 
more obvious matters demanded immediate attention. It is to be hoped 
that the line suggested will receive earlier attention, though many years must 
elapse before results of practical value are obtained. 
