84 CENTRAL AMERICAN RUBBER TREE. 



to have given a correct impression of the percentage of rubber planting 

 enterprises which are not reliable, even if he had been able to give the 

 matter detailed investigation. No general condemnation of rubber 

 planting either by individuals or by "monthly payment" companies 

 is justified, but the certainty of success is not such that the investor 

 can afford to be careless regarding the intelligence and reliability of 

 those in whose hands he places his financial fate; and the consul- 

 general will have performed an important service to the public if his 

 statements are heeded, not as a general discouragement of rubber 

 culture, but as a counsel of caution in making tropical investments. 



CONCLUDING SUMMARY. 



The culture of the Central American rubber tree has passed the 

 experimental stage in the sense that the practicability of the agricul- 

 tural production of rubber has been demonstrated, but on the other 

 hand it has been ascertained that the tree may thrive where it will 

 yield little or no rubber. Under favorable natural conditions the 

 culture of Costilla elastica bids fair to become very profitable, but the 

 experimental determination of the factors which influence the produc- 

 tion of rubber has scarcely begun. 



In southern Mexico and Central America the regions well adapted 

 to the culture of Castilla are much more limited than has been sup- 

 posed. The presence of wild Castilla trees is not a sufficient evidence 

 that a locality is suited to commercial rubber culture. 



Differences in the yield of rubber are not due merely to the exist- 

 ence of different species and varieties of Castilla, but are also con- 

 trolled by external conditions. 



The functions of the rubber milk in the economy of the plant are 

 not well understood or agreed upon by botanists, but there are numer- 

 ous reasons for holding that in Castilla and many other plants it aids 

 in resisting drought. 



A continuous!}^ humid climate is not necessary to the growth and 

 productiveness of Castilla; the indications are rather that the quantity 

 of milk and the percentage of rubber are both increased by an alterna- 

 tion of wet and dry seasons. 



In its wild state Castilla does not flourish in the denser forests, but 

 requires more open situations. It is confined to forest regions onl} T 

 by the perishability of its seeds. 



Castilla thrives better when planted in the open than in the dense 

 forest; even young seedlings are not injured by full exposure to the 

 sun, providing that the ground does not become too dry. 



The planting of Castilla under shade or in partially cleared forests 

 is to be advised only on account of special conditions or as a means of 

 saving labor and expense. 



The loss of the leaves in the dry season may be explained as a pro- 

 tection against drought, and does not indicate conditions unfavorable 

 to the tree or to the production of rubber. 



