14 



now, in quantities, and have not been able yet to observe any injurious 

 effects on the trees. Where it has been applied frequently enough to 

 keep the ground in a measure free from weeds, a marked improve- 

 ment is noticed in the appearance of the soil, as I suppose might be 

 expected from exposing it to the air." 



In applying the arsenite spray on the rubber plantation of 

 the Pacific Development Company a considerable quantity of 

 the solution was accidentally upset near two rubber trees and 

 the leaves fell from these trees within two days apparently from 

 the poisonous effects of the arsenite. The trees, however, are 

 recovering. 



The conditions under which arsenite of soda has been applied 

 in Hawaii differ greatly from those which prevail in apple or- 

 chards in Colorado. In the first place we are applying only 

 five pounds of arsenic per acre and to soils which normally con- 

 tain no arsenic. Then, too, the rainfall in rubber plantations is 

 very high (160 to 200 inches per year). In the spraying exper- 

 iments in the Colorado apple orchards the most insoluble form 

 of arsenic was used. When washed down into the soil it, there- 

 fore, remains for a long time, gradually becoming soluble and 

 being absorbed by the roots of the trees. Arsenite of soda is an 

 extremely soluble form of arsenic. It is not known whether a 

 considerable quantity of the arsenite of soda may subsequently 

 be fixed in the soil by interaction with other chemicals found in 

 the soil. The soils in the rubber plantations, however, are ex- 

 tremely porous and are underlaid with a-a to such an extent that 

 running streams are rare. It is highly probable, therefore, that 

 the most of the arsenite of soda washed into the soil by rains is 

 carried away by the water passing through the soil. It seems 

 very doubtful whether any serious accumulation of arsenic can 

 take place in the soils of the rubber plantations so long as the 

 conditions remain as at present. It can not be questioned, how- 

 ever, that arsenic in excessive quantities in the soil is injurious 

 to nearly all forms of vegetation, and, therefore, some care 

 should be observed in not using unnecessarily large quantities of 

 the arsenical spray. ~No harmful results have thus far been ob- 

 served upon rubber or other cultivated plants in Hawaii from 



