SHADE AND RUBBER PRODUCTION. 53 



milk flow* more freely from wild Castilla on the dry Pacific slope of 

 Mexico and Central America than in the more humid 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 director 

 of a rubber plantation operating in Mexico writes as follows to the 

 India Rubber World: 



We are planting 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 from 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 shade, partial shade, and open sun- 

 light, 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 prob- 

 able that shaded and unshaded trees might need to be tapped at differ- 

 ent 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 at the time the tree is tapped. The indications are 

 that pressure attains its greatest intensity in trees which are exposed 

 for a part of the time to a relatively dry atmosphere and which are 

 accustomed, as it were, to pump water rapidly to supply the leaves. 

 Such trees may, on the contrary, yield no milk at all when the water 

 supply is deficient. It may be expected, therefore, that open culture 

 will require much more careful attention to the time of tapping. This 

 may prove a disadvantage if it requires all the trees of a large planta- 

 tion to be tapped on the same day or in the same week, hut this is not 

 likely. On the other hand, tapping at the right time would mean the 

 drawing of a larger amount of milk from a smaller cut, a saving of 

 labor, and a lessening of injury to the trees. 



The above considerations make it easy to understand also that writers 

 acquainted with humid districts commonly refer to the rubber harvest 

 as occurring in the dry season, while in the drier regions, as in Soco- 

 nusco, the beo-innino- of the rainy season is the recognized time, when 

 the tree's demand for water is largest and the internal pressure highest. 



