PLANT PHYSIOLOGY 567 



been found to deepen the green colour of the leaf and to 

 postpone leaf fall, at the same time causing the leaf to become 

 abnormally thick. The increased depth of colour was ascribed 

 by Rumm (1893) to an increase in the number of chloroplasts. 

 Increase of chlorophyll content has also been observed by 

 Frank and Kriiger (1894), Zucker (1896), Bayer (1902), and 

 Schrauder (1904). Many experiments measuring the influence 

 of Bordeaux on yield have been recorded. Ewert (1905) 

 attempted to distinguish between the influence in full sunlight 

 and in shade, but it is evident from his experiments that there 

 were too many factors uncontrolled to permit conclusions to 

 be safely drawn from his results. In 191 2 a further paper 

 recorded more satisfactory results, and it was found that 

 strengths of Bordeaux above 2 per cent, reduced the yield of 

 potatoes and radishes. The yield of some varieties of beans 

 was improved by Bordeaux, and other results obtained include 

 increase of sugar content of currants and gooseberries. There 

 is a general tendency throughout to ascribe the effects to the 

 shading provided by the spray. A full summary of the earlier 

 work is given by Butler as a preface to his paper on the subject 

 {New Hampshire Agric. Exp. Sta., 1922, Tech. Bull. 21). 

 Butler found, using radish, tomato and bean, that a reduced 

 yield generally resulted from Bordeaux and milk of lime 

 sprays, and that the transpiration per gram dry matter was 

 increased by the spray. He also concluded that the action 

 of the Bordeaux was not due to the copper, but was controlled 

 by the copper-Ume ratio, in other words by the excess lime. 

 Observations of leaf colour failed to demonstrate any constant 

 effect. Darker green plants were certainly more frequent in 

 the sprayed series, but little more could be said. The results 

 in general were very variable, and in some experiments the 

 author is reduced to expressing them as " percentage of sprayed 

 plants showing increase." For example, transpiration per 

 gram dry matter was increased by spraying in 95 per cent, 

 of the tomato plants, 69 per cent, radish, and 64 per cent, 

 bean. Cultures in sand supplied with varying nutrient 

 solutions showed that spraying produced the same effect in 

 all cases. Again, in these conditions sprayed plants transpired 

 more water. In general the higher the water content of the 

 soil the greater was the depressing effect of spray on dry- 

 matter production. Photometer experiments were carried 

 out to determine the actual proportion of light stopped by 

 Bordeaux of various strengths, but the figures given can of 

 course have only a relative significance owing to the inevitable 

 wide differences of distribution which occur in practice. How- 

 ever, it is of course realised that the spray must cast a shadow, 

 and to this may possibly be attributed the delay in ripening 



