260 



dry season could be left spread over the ground. This would do 

 more to conserve the moisture of the soil than the same vegetation 

 alive, but the danger of fire will in most localities forbid the use 

 of this method of culture." 



"With shade recognized as a means of influencing natural 

 conditions of soil or climate it becomes evident that each planter 

 will need to use his best judgment in determining what local 

 conditions require. In Costa Rica, Koschny advises the thinning 

 of the forest by the removal of two or three trees out of every five. 

 At La Zacualpa more are cut out. Some of the planters on the 

 Isthmus of Tehuantepec practice clean culture. No general 

 principles will determine which is best, because no one method is 

 applicable everywhere. 



AGE AT WHICH TREES MAY BE TAPPED.* 



"The earliest age at which Castilloa trees may be tapped with 

 safety and advantage has been stated all the way from four to 

 twelve years, while from eight to ten years is the conservative 

 estimate. At the same time it must be admitted that little in the 

 way of positive knowledge exists on this point, and careful 

 experiments may be necessary to determine whether, for example, 

 the taking of half a pound of rubber from each tree in the sixth 

 year will retard growth so as to diminish the yield of succeeding 

 years. As the trees approach maturity and have occupied most of 

 the available space, as much may be taken as will not weaken the 

 tree and shorten its life. 



"The inferior quality of the rubber obtained from young trees 



also lessens the inducement for tapping them. It has been known 



for several years that the rubber and gutta-percha obtained from 



young plants or from the leaves and twigs of the trees is different 



from that yielded by the trunk of mature age, in that a smaller or 



larger percentage of rubber is replaced by non-elastic, brittle, or 



sticky substances commonly referred to as "resins." Dr. C. O. 



Weber has recently published the following results of analyses of 



samples of rubber from trees varying in age from two to eight 



years : 



Resins in rubber from trees. Per cent. 



2 years old ... 42'33 



3 do ... 3502 



4 do ... 26-47 



5 do ... 1818 



7 do ... 11-59 



8 do ... 7'2I 



"The same writer also gives a table showing the varying 



amount of resin in samples from different parts of the same tree : 



Resin in rubber from— Per cent. 



Trunk ... 2-61 



Largest brancfies .. 377 



Medium do ... 4'88 



. Young do ... 5-86 



Leaves ... 7'50 



♦ Extracts from Bull. No. 49, U. S. Dept. of Agri. 



