79. BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE. 
stems, and roots of the sprayed potato plants than in those of the 
unsprayed plants. : 
(¢) Variations in sunlight or stimulation resulting from the appli- 
cation of copper sprays may influence the photosynthetic processes. 
(d) The copper sprays protect the vines which are thus kept freer 
from tip burn, disease, and insect injury. Vines treated in this way 
are therefore more vigorous and their tubers may show an increase 
in solids, as well as in yield. It is now recognized that potato leaf- 
hoppers are the direct cause of hopperburn and that Bordeaux 
mixture repels the hoppers. Bordeaux spray is a protection against 
potato leafhoppers, flea beetles, and other insects, as well as against 
fungous diseases. It is not clear why the tubers should be higher in 
solids unless it is simply taken for granted that a vigorous plant 
produces a tuber higher in solids than a less vigorous plant. There 
is a possibility that the protective effect of Bordeaux is the only effect 
produced, but copper salts have such a pronounced effect on all living 
tissue that a stimulation is generally suspected and even accepted by 
many investigators in this field. 
Some suggestions from the recent work of Sherman and his co- 
workers are of interest in this connection. They studied the effects 
of certain antiseptics upon the activity of amylases (42), all of which 
were very sensitive to copper sulphate. They also studied the influ- 
ence of certain amino acids upon the enzymic hydrolysis of starch 
(43), finding that glycine, alanine, phenyl! alanine, or tyrosine caused 
an undoubted increase in the rate of hydrolysis of starch by purified 
pancreatic amylase, commercial pancreatin, saliva, or purified amy- 
lase. The favorable effect is not due to any influence on hydrogen 
ion concentration nor to a combination of the amino acid with the 
product of the enzymatic reaction. The addition of 1 per cent of 
these amino acids was shown to be a very effective means of pro- 
tecting the enzyme from the deleterious eftect of copper sulphate and 
may even serve to restore to full activity any enzyme which has been 
partially inactivated by copper. Arginine and cystine have a favor- 
able influence upon the hydrolysis of starch by purified pancreatic 
amylase, while histidine and tryptophane do not (j4). The effect 
of histidine and tryptophane differs from that of all the other amino 
acids studied, possibly because of their heterocyclic structure or their 
position in the protein complex which doubtless constitutes either 
the enzyme itself or an essential part of it. 
There is evidence that a somewhat larger quantity of copper is 
present in copper-sprayed potato plants than in the unsprayed plants, 
and also that the proportion of amino and amid nitrogen in potato 
plants increases during growth. Data showing that copper had a 
favorable effect on the yield and composition of tubers were obtained. 
Possibly the amino acids protect the cell activity from any toxic 
action of the copper, thus permitting the copper to exert a stimulating 
effect on the cells. 
It is recognized that it would be desirable to have data showing 
the normal variation for the different varieties of tubers under the 
same conditions, but time did not permit the securing of such data. 
Analyses of several hundred tubers, both copper-sprayed and check, 
were obtained and the average data from this large number of tubers 
should overcome individual variation. 
