i8 



ment of lateral branches, nor even in the lessening of the size of 

 the individual trees, but in the decrease in the amount of rubber 

 which can be produced on a given area of land, 



SHADE AND RUBBER PRODI'CTION. 



The general question of shade can not, however, be treated as 

 closed until its influence on the yield of rubber has been tested by 

 careful experiment. From the facts given on previous pages it 

 appears very improbable that less rubber will be formed in the 

 open than under shade ; the difficulty, if any, is likely to arise in 

 connection with the extraction of the rubber. The desirability of 

 tall trunks to afford a large tapping surface has been noted al- 

 ready, but there may be other disturbing factors. The pressure of 

 the liquids inside a tall columnar trunk ma}'" be greater than if it 

 were thicker and shorter, so that more milk would be forced out 

 on tapping. The bark of trees more exposed to wind and sun- 

 light becomes thicker and there may be differences in texture 

 which would affect the flow of milk. The air is much dryer out- 

 side than inside the forest, and this might soon impede the flow 

 of milk, though this suggestion seems to be negatived by the fact 

 that milk flows more freely from wild Castilloa on the dry 

 Pacific slope of Mexico and Central America than in the more hu- 

 mid districts of the Atlantic side. 



A recent writer on the shade question claims to have discovered 

 that, while planting under partial shade hinders the growth of the 

 trees, it greatly increases the yield of rubber. The managing di- 

 rector of a rubber plantation operating in Mexico writes as fol- 

 lows to the India Rubber World : 



We are plaiitin;^ in the partial shade ; a great many planters are planting in 

 open sunlight. My honest opinion is that every one who has planted in open 

 sunlight will get a tree 50 per cent larger in five or six years than we in the partial 

 shade. On the other hand, we will get fr< m 60 to 75 per cent, more rubber from 

 a small tree than they do from a large one. About three months' careful study 

 was made of this proposition ; the trees were tapped both in the -hade, partial 

 shade, and open sunlight, and the results carefully tabulated by a committee of 

 which I was not a member. 



It is easy, however, to understand how such an opinion could be 

 formed if the experiments in tapping were made at a time when 

 the trees planted in the open were drier than those in the shade, 

 and such a difference would be especially pronounced in young 

 trees. This observer did not find that the milk was richer in 

 rubber in the shade, but merely that at a certain time more milk 

 flowed from the shaded tree than from the unshaded tree. This 

 would not, however, be an argument for shade planting unless it 

 were shown that the unshaded trees would not at any other time 

 yield more milk. It is quite probable that shaded and unshaded 

 trees might need to be tapped at different times to secure a 

 maximum flow, or it might be found that unshaded trees could be 

 tapped with impunity more frequently than the others, and thus 

 afford a larger annual yield. The flow of milk does not depend 

 so much upon the amount in the tree as upon the pressure existing 



