CONCLUDING SUMMARY. 85 



The falling of the leaves of Costilla elastica in the dry season ren- 

 ders it unsuitable as a shade tree for coffee or cacao. In continuously 

 humid localities where the leaves are retained shade trees are super- 

 fluous and the } T ield of rubber declines. 



The desirable features of shade culture, the shading- of the soil, and 

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

 the rubber trees closer together rather than by the use of special 

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

 expediency. 



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

 ishes during the wet. The flow of milk is lessened in dry situations 

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

 trees yield milk much more 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 Castilla may 

 be undertaken in more salubrious regions than those to which rubber 

 production has been thought to be confined; the experimental planting 

 of Castilla in Porto Kico and the Philippines becomes advisable, but 

 extensive planting in untried conditions is hazardous. 



No satisfactory implement for the tapping of Castilla trees has come 

 into use. Boring and suction devices are excluded by the fact that 

 the milk is contained in fine vertical tubes in the bark, which must be 

 cut to permit the milk to escape. 



In British India it has been ascertained that the Para rubber tree 

 ma}- be repeatedly tapped on several successive or alternate days by 

 renewing the wounds at the edges. The yield of milk increases for 

 several tappings and the total is unexpectedly large. It is not yet 

 known whether multiple tapping is practicable with Castilla, or 

 whether this new plan nia} T not give the Para rubber tree a distinct 

 cultural advantage over Castilla. 



The gathering of rubber from trees less than eight years old is not 

 likely to be advantageous; the expense of collecting will be relatively 

 large, and the quality of such rubber is inferior, owing to the large 

 percentage of resin. 



The rubber of Castilla is scarcely inferior to that of Hevea. The 

 supposed inferiority is due to substances which can be removed from 

 the milk b} T heat and by dilution with water. 



