﻿COPPER SPRAYS ON IRISH POTATO TUBERS. 9 



The proportion of solids in most cases showed a gradual increase 

 during the growth of the tubers. With the exception of the Green 

 Mountain sample, the proportion of solids was higher in the tubers 

 from copper-sprayed plants than in those from the unsprayed plants 

 at the time of the first analysis, that is, when the tubers were less 

 than an inch in diameter. This indicates that the effect of the copper 

 was exerted very early in their development. 



The solids for all the tubers from the Bordeaux-sprayed plants 

 averaged 18.63 per cent; for all those from the unsprayed plants, 

 17.87 per cent ; for all those from barium- water-sprayed plants, 19.58 

 per cent; and for all those from Pickering-sprayed plants, 18.29 per 

 cent. 



The following average ash figures were obtained for all the samples 

 analyzed: Tubers from unsprayed vines, 0.87 per cent; tubers from 

 Bordeaux-sprayed plants, 0.88 per cent; and tubers from Pickering- 

 sprayed plants, 0.85 per cent. The percentage of the total ash found 

 as insoluble ash decreased in most cases during the growth of the 

 tubers. 



The pH data obtained on the water extracts of the tubers showed 

 no significant change. 



The proportion of total nitrogen, which increased during the 

 growth of all four varieties of tubers, was somewhat higher for the 

 tubers from copper-sprayed plants than for those from the un- 

 sprayed plants. The percentage of nitrogen was higher for the 

 tubers from copper-sprayed plants than for those from the unsprayed 

 plants at the time of the first analyses, showing again that the action 

 of the copper on the metabolic activities of the plant was exerted 

 very early. 



The percentage of insoluble nitrogen in the tubers showed a tend- 

 ency to decrease during growth. The percentage of soluble nitrogen 

 increased during growth. The percentage of coagulable nitrogen 

 increased during growth in the case of the Irish Cobbler, the Early 

 Ohio, and the Early Rose varieties, but not in the Green Mountain 

 variety. The monoamino and amid nitrogen, which includes the 

 nitrogen not precipitated by phosphotungstic acid, showed a marked 

 increase for all four varieties during growth. The average per- 

 centage was slightly higher in the tubers from copper-sprayed plants 

 than in those from the unsprayed plants. The ammonia nitrogen 

 content showed no regular change. 



During tuber development the percentage of starch increased some- 

 what more rapidly than the percentage of solids. A larger percent- 

 age of starch was usually found in the tubers from copper-sprayed 

 plants from the first analysis to the last than in the check tubers. 

 The average data for the content of starch in the tubers were : Bor- 

 deaux-sprayed, 12.24 per cent; check, 11.73 per cent; barium-sprayed, 

 12.67 per cent ; and Pickering-sprayed, 12.36 per cent. 



The sugars, calculated as dextrose and sucrose, were present in the 

 young tubers in relatively large proportions. At the time the tubers 

 had reached maturity the dextrose had practically disappeared and 

 the quantity of sucrose had markedly decreased. The unsprayed 

 tubers of the three early varieties contained a higher percentage of 

 sugars in the first stages of development and usually a lower per- 

 centage at maturity than the tubers from copper-sprayed plants. 



27475°— 23 2 



