ORCHARD SPRAYING i;XPERIMe;nTS. 2>7 



Apples are more resistant to injury than peaches. 



The factors necessary to the production of injury appear to 

 be water on the leaves, high atmospheric humidity, shade and 

 an excess of plant respiration over carbon dioxide assimilation. 



His theory is, that under proper conditions of minimum light 

 intensity, the carbon dioxide of respiration exceeds that of 

 assimilation and escapes through the stomata where, dissolving 

 in water on the leaves, it brings the copper of the bordeaux 

 mixture into solution. Such solvent copper enters the leaves 

 by diffusion through the stomata and causes death of the cells. 



The solvent action of plant secretions upon bordeaux mixture 

 mentioned by Hedrick as a possible causative agent in bordeaux 

 injury of the apple is doubtless offered on the strength of an- 

 alogous experiments of Schander* with bordeaux in its relation 

 to Fuchsia and Oenothera and also with Phaseolus multiflorus. 



This work is cited by both Hedrick and Crandall. Schander 

 ascribes all bordeaux injury to the action of secretory organs 

 upon the copper hydroxide. Crandall, in commenting on this, 

 points to the fact that no proof of the solvent action of secre- 

 tory organs upon bordeaux has been demonstrated in the case 

 of the apple. The possibilities, as Crandall notes, are in favor 

 of a combination of many of the factors heretofore- regarded 

 as solvents of the copper in the mixture ; the physiological fac- 

 tor recently submitted by Groth appears to be a vital one in 

 arranging experiments where the conditions of control shall be 

 well assured. 



Leaf injury has in all cases, so far as known, been ascribed 

 to the entrance of copper in solution into the leaf tissues. How 

 this toxic agent comes in contact with the tissues finally de- 

 stroyed is a question regarding which there is a difference of 

 opinion. One theory of imbibition and osmosis held by a group 

 of prominent foreign- investigators is opposed to the chemotactic 

 theory of others.** 



Crandall has rightly emphasized the necessity of isolating 

 and determining, if possible, the group of factors now held 

 responsible for injury under the general heading of atmospheric 



*Schander, R. "Ueber die Physiologische Wirkung der Kupfervit- 

 riolkalkbriihe." Landwirtschaftliche Jahrbiicher 23, PP- 517-584- (1904.) 



**For a detailed account of these theories and the experiments on 

 which they are based, see Crandall {loc. cit. pp. 228-232). 



