THE EFFECT OF SURFACE FILMS AND DUSTS ОХ THE 
RATE OF TRANSPIRATION 
B. M. DUGGAR 
Physiologist to the Missouri Botanical Garden 
Professor of Plant Physiology in the Henry Shaw School of Botany of 
Washington University 
AND J. S. COOLEY 
Rufus J. Lackland Fellow in the Henry Shaw School of Botany of 
Washington University 
The fungicides commonly employed are either in the form 
of solutions (e. g., ammoniacal copper carbonate), suspensions 
(lime wash and Bordeaux mixture), and powders (sulphur). 
The use of spray mixtures or other fungicides has become 
world wide, and many problems of physiological interest have 
arisen respecting the effects of these substances on the plants 
which they are designed to protect. Bordeaux mixture has 
been under continuous observation for a period of about twenty 
years, and has proved interesting in both its toxic and other 
relations. The striking influence of this fungicide upon sound 
plants has awakened widespread interest, and numerous 
experiments have been made to determine the nature of the 
effects. Bordeaux mixture consists essentially of suspension 
films of copper hydroxid and certain other complex (mostly 
hydrated), largely insoluble, copper compounds; and when 
properly sprayed upon plant surfaces from the best nozzles, 
the particles are of extreme fineness, and there is realized an 
almost perfect surface film. In spite of the greatest care in 
preparation and application, it is injurious to certain plants, 
such as the peach and the plum, and may not be used satis- 
factorily in such cases for disease control. In recent years it 
has been shown that the extent of the injury to the apple and 
other plants may be considerable, and Bordeaux mixture is 
in such cases being supplanted. In this discussion, however, 
we may omit any detailed consideration of the toxic effects. 
of this mixture, a phase of the subject which has received much 
consideration in this country from Bain (2), Crandall (6), Clark. 
Ann. Mo. Bor. Garp., VoL. 1, 1914 (1) 
