﻿22 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE. 



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stems, and roots of the sprayed potato plants than in those of the 

 unsprayed plants. 



(c) 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 

 arc 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- 

 worker's are of interest in this connection. They studied the effects 

 of certain antiseptics upon the activity of amylases (4@), 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 

 (4$), 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 effect 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 (44)- 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. 



