34 S. E. A. McCallan 



action by the spores toward the bordeaux mixture is entirely possible. 

 Schmidt's failure, in his first experiment, to obtain soluble copper from the 

 sprayed bordeaux, is not in entire accord with his general conclusion, and 

 also points to a delay in fungicidal action, which has been definitely estab- 

 lished not to be the case. 



In summarizing the literature on the action of atmospheric agencies, it 

 should be emphasized that a great many of the experiments were performed 

 with freshly made bordeaux mixture or other copper suspensions before 

 they had been dried, as is the case when applied to plants. This evidence, 

 therefore, can have no conclusive bearing on the liberation of copper from 

 fungicides after they have been dried on the plant. Nor should the action 

 of excessive quantities of CO2 be taken as a criterion for judging the prob- 

 able action of the very small quantities present in the atmosphere. There 

 seems to be convincing evidence that meteoric waters possess a solvent 

 action not exhibited by distilled water. Whether this difference is due 

 solely to the CO2 content has not been demonstrated. Under field condi- 

 tions, with the plants exposed to the rain and dew, copper appears to be 

 brought but slowly into solution from " insoluble " copper protectants. 



STJSCEPT EXCRETIONS 



The hypothesis that excretions from the sprayed plant (the suscept) 

 exert a solvent action on the insoluble copper protectants, has received but 

 little attention. From the mass of literature on injury and the physio- 

 logical relations of bordeaux mixture and the suscept, there may be gath- 

 ered a little direct experimental evidence relative to the solvent action of 

 suscept excretions. The author makes no claim to having thoroughly 

 reviewed this literature. 



Swingle (1896:20) states: " It is possible that the drops of rain or dew 

 standing for some time on the leaves or other parts of plants may absorb 

 from superficial cells sugar or other substances that may serve to increase 

 t lie solubility of the copper." Some observations of previous writers which 

 led Swingle to suggest this hypothesis are presented. 



Clark (1902) applied a spray of excess-lime bordeaux mixture to a peach 

 tree. Following this, the tree was sprayed several times with " pure " 

 water, to give the effect of dew. On the following day, water collected 

 from the leaves showed the presence of a slight amount of soluble copper. 

 Branches containing some of these leaves were placed in distilled water, 

 and after some hours soluble copper was detected. Clark believes that 

 there is an exosmosis of some of the contents of the cell sap, which, coming 

 in contact with the bordeaux adhering to the leaf surface, cause more or 

 less copper to become soluble. One is hardly justified, however, in draw- 

 ing such a general conclusion from a limited experiment. 



Bain (1902), studying bordeaux injury to peaches, performed a few 



