566 SCIENCE PROGRESS 



increase varied with the nature of the film. A further observa- 

 tion was that the influence was greater on detached leaves 

 than on potted plants. The accelerating influence was found 

 to be greatest immediately after the drying of the spray. 

 The evidence for an increased transpiration rate following 

 Bordeaux spraying v/as completed by Shive and Martin 

 {Plant World, 191 7, 20, 67-86), who used the hygrometric 

 paper method to test tomatoes growing in the open, and were 

 able to confirm the results obtained by Duggar and Cooley 

 and by Martin. In addition Shive and Martin observed that 

 the accelerating influence of the spray was effective whether 

 climatic conditions were such as tended to produce high or 

 low transpiration rates. Further analysis of the transpiration 

 problem was attempted by Duggar and Bonus {Ann. Mo. 

 Bot. Gard., 1918,5, 153-76), who used potted potatoes, tomatoes, 

 marguerites, tobacco and Cy perns, and took special precautions 

 to ensure that all plants in a series were subject to identical 

 environment. Increased transpiration rates due to Bordeaux 

 spraying were again demonstrated in mesophytes, and, more- 

 over, it was found that practically the whole of the observed 

 increase took place during the night intervals. In this fact 

 the authors consider they have found the clue to the mechanism 

 of the acceleration. At night, in a greenhouse with the usual 

 temperature and humidity fluctuations, many plants are in a 

 state of guttation or incipient guttation, and it is supposed 

 that a film of dried Bordeaux would under these conditions 

 act as a bibulous layer, spreading the guttation water and 

 thereby causing a greater loss. During the day, in the absence 

 of guttation, the stomata function normally and the surface 

 film no longer asserts its bibulous nature. No accelerating 

 effect was found in the case of Cyperus, and the authors believe 

 that the minute size of the stomata and intercellular spaces 

 in this plant results in the clogging of the pores with a conse- 

 quent occasional transpiration decrease. In the case of 

 excised leaves it is not certain, of course, that a state of gutta- 

 tion is established as frequently as in growing plants, even 

 if such a state exists at all, so that, pending further work, the 

 explanation of results obtained with detached leaves is still 

 in abeyance. 



The work on transpiration has served clearly to show that 

 the Bordeaux influence is very much subject to climatic and 

 environmental conditions generally, and also to the nature of 

 the plant treated. 



With regard to the influence of Bordeaux spray on other 

 physiological functions of the plant, work has been in progress 

 for nearly thirty years, the main results of which need be 

 summarised only very briefly here. In general, spraying has 



