4 o8 SCIENCE PROGRESS 



a similar size. The yields from estates planted with these 

 two trees bear this out in a striking manner. 



The planting of Castilloa in Mexico, as already mentioned, 

 commenced a year or two in advance of that of Hevea in the 

 East. Wound-response not being then known, the former 

 seemed the more promising tree, as it yielded its latex with 

 greater ease. At the present time, however, little is heard of 

 Castilloa plantation rubber, while that of Hevea is making a 

 sensation unparalleled in the history of tropical agriculture. 

 This is wholly due to the advantage taken of the wound- 

 response, which appears totally absent in Castilloa. The one 

 gives pounds of rubber per annum, whilst the other gives ounces. 



The latest accounts 1 of Castilloa in Mexico are not over- 

 encouraging, but with rubber at anything like its present price, 

 the estates now coming into bearing will doubtless prove 

 remunerative. A six-year-old Castilloa apparently gives only 

 2 to 3 oz. of rubber in the year without seriously injuring 

 the tree, whereas a Hevea of similar age will yield about a 

 pound. At ten years old the proportion appears to be about 

 4 or 5 oz. for Castilloa and 3 to 4 lb. for Hevea. It seems 

 that the more Castilloa has been studied from the economic 

 standpoint, the less satisfactory it becomes, while, on the con- 

 trary, Hevea has ever continued to grow in favour. 



This phenomenon of wound-response in Hevea is not only 

 of great practical importance in rubber cultivation, but is also 

 of considerable botanical interest, and requires more extended 

 investigation. To what circumstances is the increased flow of 

 latex arising from injury due ? In Hevea the milk (laticiferous) 

 tubes reside chiefly in the innermost third of the bark, i.e. in the 

 youngest and most functional part of the bast (phloem). New 

 tubes are continually being formed in the fresh phloem, produced 

 by the actively dividing layer of cells, the cambium; these take 

 the place of the older exterior tubes, which become compressed 

 and eventually obliterated by the tree's expansion. If the latici- 

 ferous tubes in a definite area of bark were completely drained of 

 their contents, two possibilities might happen. On the one hand, 

 this region might yield little or no latex, until the cambium 

 formed new tubes — a process occupying some time ; or, on the 



1 India- Rubber Journal, 1909, vol. xxxvii, p. 701. An article on Castilloa 

 cultivation in the Quarter-century No. (p. 85) of this Journal gives higher 

 yields —viz. about half those of Hevea. 



