6 BULLETIN 1146, U. 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 stomata 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 (74) 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 
potato 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 (7/5) decided that Bordeaux apphed 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 New 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- 
perburn” 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. 
