4 BULLETIN 785, U. S. DEPARTMENT OF AGRICULTURE. : 
The analytical data are based on the dry weight of the samples, and 
the field tests data have been converted to the same basis by assuming 
a constant value of 35 per cent for the dry weight of the leaves (fig. 1). 
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Fic. 1—Tests for copper on apple leaves sprayed with 34-50 Bordeaux mixture. A represents 
the results of chemical analyses on the basis of milligrams per 1,000 grams dry weight of leaves. 
B represents the results of field tests of duplicate samples on the basis of milligrams per 100 grams fresh 
weight of leaves. The two scales are plotted on an equivalent basis, assuming the dry weight of the 
leaves to be constantly 35 per cent. 
A scale for equivalent readings in milligrams of copper per 100 grams 
fresh weight of leaves is also indicated in the figure. 
At this early period in the work the samples were too small to give 
the best results for so large a planting. However, there is reasonably 
close agreement between the graphs secured by the two methods, with 
the exception of a few of the first determinations. 
Tests were made during July and August, 1917, in two apple or- 
chards, A and B, at Crozet Va., sprayed by the owners with 34-50 
Bordeaux mixture according to their usual practices. Both orchards 
