102 



culture of Castilloa* elastica bids fair to become very profitable, but 

 the experimental determination of the factors which influence the pro- 

 duction of lubber has scarcely begun. 



In Southern Mexico and Central America the regions well adapted 

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

 posed The presence of wild Castilloa 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 Castilloa, 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 Castilloa and many other plants it 

 aids in resisting drought. 



A continuously humid climate is not necessary to tl e growth and 

 productiveness of Castilloa ; the indications are rather that the quan- 

 tity of mdk and the percentage of rubber are both increased by an 

 alternation of wet and dry seasons. 



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

 but requires more open situations. It is confined to forest regions 

 only by the perishability of its seeds. 



Castilloa 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 Castilloa under shade or in partially cleared forests 

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

 savipg labour and expense. 



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

 protection against drought, and does not indicate conditions unfavour- 

 able to the tree or to the production of rubber. 



The falling of the leaves of Castilloa ela-tica in the dry season ren- 

 ders it unsui able f-s a shade tree for coffee or cocoa. In continously 

 humid localities where tl e leaves are retained shade trees are superflu- 

 ous and the yield of rubber declines. 



The desirable features of shade culture, the shf:ding of the soil, and 

 the encouragement of tall upright trunks, are to be secured by plant- 

 ing the rubber trees closer together rather ihan by the use of special 

 shade trees. Planting closer than 10 feet, however, is of very doubt- 

 ful expediency. 



The percentage of rubber increases during the dry season and di- 

 minishes during the wet. The flow of milk is lessened in dry situa- 

 tions by inadequate water supply, but at the beginning of the rains 

 such trees yield milk much moie freely than those of continuously 

 humid localities. The claim that more rubber is produced in the 

 forest or by shaded trees seems to rest on tapping experiments made 

 in the dry season. 



Continuous humidity being unnecessary, the culture of Castilloa 

 may be undertaken in more salubrious regions than those to which 

 rubber production has been thought to be confined ; the experimental 



* Prof. Cook prefers the spelling Castilla, 



