PLANT PHYSIOLOGY 565 



apart from any effect on the amount of the total crop. No 

 explanation is offered as to whether this is merely a negative 

 influence brought about by the reduction of fungal infection, 

 or whether it is a direct effect upon the tree itself. 



The general physiological result of Bordeaux spray is 

 expressed in the phrase " greater longevity," and frequent 

 cases of this have been observed and recorded. References 

 to the earlier literature will be found in the majority of the 

 papers quoted below. Clinton in 1909 was the first to refer 

 this increased longevity to the water relations of the plant. 

 His explanation was that the film of sediment from the spray 

 clogged stomata and hydathodes and thereby reduced water 

 loss. His reasons were (i) the absence of " tip burn " in dry 

 seasons from sprayed plants, and (2) the observation that 

 sprays with little sediment did not prolong the life of the 

 plant. Other workers at the time subscribed to this idea, 

 but careful experimental work almost immediately afterwards 

 showed that exactly the reverse was in fact the case, namely, 

 transpiration was actually increased by spraying. Duggar 

 and Cooley in more recent years have attacked the problem 

 with the better methods now available, and have published 

 a series of papers. In the first work {Ann. Mo. Bot. Gard., 

 1 914, 1, 1-22) they used Ricinus leaves in potometers and 

 tomato plants in pots, and found considerably higher transpira- 

 tion rates in sprayed than in unsprayed Ricinus leaves. The 

 same result was obtained with the potted tomatoes, and in 

 this case, in addition, data were collected showing that various 

 other surface films besides Bordeaux may produce in some 

 degree the same effect. Among the substances used to produce 

 the film were Ca(0H)2, A1(0H)3, clay, charcoal, CaCOg and 

 lime-sulphur mixture, but the results obtained, although 

 showing differences from the controls, hardly warrant anything 

 but a tentative conclusion. The same remark applies to the 

 water requirement figures for tomato, which vary from 13*1 

 (sprayed with charcoal) to 11 -8 [Ca(0H)2] with the control 

 giving 12*1. The same authors report a trial with potted 

 potatoes {Ann. Mo. Bot. Gard., 1914, 1, 351-6) which gave 

 quite similar results, the transpiration from plants sprayed 

 with weak Bordeaux being 50 per cent, greater than from the 

 controls. Martin {Journ. Agr. Res., 191 6, 7, 529-48) repeated 

 the experiments of Duggar and Cooley under different con- 

 ditions in a different locality. Using a variety of species at 

 different times, Martin found that the average transpiration 

 increase due to Bordeaux spraying, for all plants used, was 

 about 100 per cent., with the extremes of 37 per cent, for 

 Datura metaloides and :ij2 per cent, for Hibiscus cardinalis. 

 He also agreed with the earlier workers that the extent of the 



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