LATEX AND CLIMATE. 39 



The greater humidity of the atmosphere would also tend to the con- 

 tinuation of the flow in the rainy season by preventing the drying or 

 the coagulating of the surface of the cuts, though the importance of 

 this factor has not been determined. 



That the increase of the rubber content of the latex serves as a 

 protection against drought is also rendered somewhat more probable 

 by the fact that Castilla has several characters serving the same pur- 

 pose. The development of hairs upon the branches, bud scales, 

 leaves, flowers, and fruits is much greater than is usual among related 

 plants. The self-pruning of the branches and the rapid covering of 

 the scars are also exceptional and of obvious utility in reducing trans- 

 piration, and the prompt falling of the leaves in situations where the 

 water supply becomes deticient shows even better the sensitiveness of 

 Castilla to drought. 



SIGNIFICANCE OF MULTIPLE TAPPING. 



The latex problem acquires new interest from the recent demonstra- 

 tion that Hevea, at least, continues not only to yield milk by the daily 

 renewal of the wounds, but that the quantity actually increases for 

 several days. This might seem to favor the idea that the latex has a 

 nutritive function, the additional quantities being assembled, as it 

 were, to repair the injury. On the other hand, the supposition that the 

 rubber hinders evaporation would also work equally well and affords 

 the additional suggestion that the greater evaporation from the wound 

 may assist in collecting the rubber about it, the yield increasing as the 

 widening of the wound increases the surface of evaporation until the 

 available supply of latex has been depleted. 



CLIMATE AND RUBBER PRODUCTION. 

 A CONTINUOUSLY HUMID CLIMATE NOT NECESSARY FOR CASTILLA. 



The study of Castilla furnishes evidence that with this tree there is a 

 relation between climate and rubber production, and that this relation 

 is the opposite of that commonly supposed to exist. 



The vast quantity and high quality of Para rubber have naturally 

 given Brazil the chief place in the thoughts of those interested in rub- 

 ber, and it is one of the best established traditions of the subject that 

 the native home of rubber is in the vast, periodically overflowed val- 

 leys of the Amazon and its tributaries; and the common failure to 

 appreciate the diversity of the rubber-producing trees gave this idea 

 very general acceptance. 



Practical experiments in Central America soon showed, however, 

 that Castilla will not thrive in swamps or where the drainage is defi- 

 cient, and this fact is generally noted as a cultural difference between 

 Castilla and Hevea, though the need of continuous humidity for Cas- 

 tilla is still insisted upon. The point has even been carried so far that 



