﻿6 BULLETIN lUli. V. S. DEPARTMENT of agriculture. 



stimulation resulted. He found a diminished assimilation by the 

 sprayed leaves for a time. This effect, however, gradually disap- 

 peared. It is suggested that the stomala are blocked by the Bordeaux 

 mixture, so that less air is diffused into the intercellular spaces and 

 less carbon dioxid comes into contact with the absorption surfaces. 

 This then is a mechanical and not a physiological action that reduces 

 assimilation. 



Duggar and Cooley (14) showed that potted potato plants when 

 sprayed with Bordeaux transpire more water than unsprayed plants. 



Duggar and Cooley (14), using potted potato plants, studied the 

 effects of surface films on the rate of transpiration. The use of Bor- 

 deaux and other films increased the rate of transpiration. The plants 

 treated with weak Bordeaux (2-3-50) were in good condition at 

 the close of the test, while those sprayed, with stronger Bordeaux 

 (4-6-50) showed injury from too much transpiration. These in- 

 vestigators stated that it does not follow that the same results will be 

 obtained in the open. 



After measuring the cells of Bordeaux-sprayed and unsprayed 

 j^otato leaves, Lutman (33) concluded that in general the leaves 

 from the Bordeaux-sprayed plants had thicker palisade and pulp 

 parenchymas than those from the check plants. He believed also that 

 the number of chlorophyll bodies was increased in the sprayed leaves. 

 An increased turgor is probably the immediate cause of these un- 

 usually large cells. He considered that a small quantity of copper 

 enters the leaf and that a chemical combination takes place between 

 the chlorophyll and the copper. The chlorophyll is less easily re- 

 moved from sprayed plants, showing that it has been rendered less 

 soluble. Greenhouse tests and experiments conducted for one year 

 in Germany by Lutman showed no stimulation effects. Lutman con- 

 siders that in this country the physiological effects of Bordeaux on 

 the potato are quite as important as its fungicidal effects. The 

 physiological effect observed in Vermont is ascribed to lessened tip 

 burn and flea-beetle injury and not to a stimulation and daily 

 increase of starch formation as suggested earlier by him. 



Edgerton (15) decided that Bordeaux applied in Louisiana de- 

 layed the ripening of tomatoes, while any increase in yield was un- 

 certain. Pritchard and Clark (38) concluded that treatment with 

 copper sprays increased the yield of tomatoes in Virginia, Mary- 

 land, Indiana, and Xew Jersey. 



In some of Montemartini's experiments (36) one side of a plant 

 was sprayed while the other was not. Leaves sprayed in the morn- 

 ing with dilute copper sulphate solution and removed and measured 

 in the evening had a greater dry weight per unit area than the 

 untreated leaves. When leaves were treated at night and removed 

 in the morning they had a lower dry weight per unit area than the 

 untreated leaves. According to Montemartini, these results indi- 

 cate that the treatment stimulated the formation and translocation 

 of organic matter. 



Ball (5) has definitely established the fact that the potato leaf- 

 hopper causes "burning of potato leaves, to which the term "hop- 

 perbum" has been applied. He states also that it has long been 

 recognized that spraying with Bordeaux mixture reduces tip burn, 

 probably because it acts as a partial repellent against the leafhoppers. 



