362 The Principles of Fruit-growing 



an appreciable injury either to the roots of plants or to 

 the soil." 



Recent studies lead Headden to conclude, in conditions 

 in Colorado, that the plant may take up the arsenic, that 

 the arsenical preparations used in spraying are water- 

 soluble to some extent, and that the tree may be injured 

 and killed by the action of arsenic collected about the 

 crown or collar (Colo. Bull. Nos. 131, 157). Arsenic was 

 found in plant tissue and soluble arsenic was detected in 

 the soil. "Three forms of this trouble were recognized, 

 corrosive arsenical poisoning, systemic arsenical poisoning, 

 and arsenic-lime poisoning. The last form is considered 

 as being produced by the joint action of lime and arsenic, 

 because we do not find this trouble present on limestone 

 soils in general, nor is it characteristic of arsenical poison- 

 ing produced by soluble arsenic preparations, sodic 

 arsenite, for example." 



The subject of soil-poisoning by arsenical materials 

 used in spraying is now again under discussion. It needs 

 to be worked over under many conditions. Similar in- 

 juries are those of crown-rot due, perhaps, to winter injury, 

 and there may be confusion between these injuries and 

 those attributed to arsenic poisoning. Ball and Titus have 

 found (Journ. Econ. Ent. Ill, pp. 187-197, 1910) that 

 arsenic can be packed about the roots or trunks without 

 injury. The subject will have increasing importance, as 

 the arsenical materials are used more liberally and as they 

 accumulate in the soil. Whether there is danger of injury 

 to trees in humid regions is to be determined by investi- 

 gations in many places. 



It is a good commentary on the certainty and regu- 

 larity of spraying, and the control of the processes, that 



