1914] 
DUGGAR AND COOLEY— FILMS AND TRANSPIRATION 9 
found necessary to insert in each pot a small bent tube in order 
to provide for the changes in air pressure. 
The pots were weighed at the beginning and at the close 
of the experiment, but the condition of the plant and the amount 
of water entering readily from the thistle tube were found 
adequate to indicate the daily water requirements. То the 
total provisional transpiration quantities obtained from a 
summation of the quantities daily added, the differences in 
weight between the beginning and the close of the experiment 
were added or subtracted as required. From five to ten plants 
were employed with each kind of spray or dust used, and the 
plants of each lot were so distributed in the greenhouse that 
an equal number—so far as possible—from every group was 
subject to exactly the same influences. Moreover, positions 
in the greenhouse were shifted several times during the obser- 
vation intervals of from ten days to two weeks. As a result 
of a large amount of experimental work in the greenhouse 
it has become apparent that the points just referred to are 
important. Plants situated nearer the edges of the benches, 
or those which receive drafts from opening doors or from 
convection currents, show considerable differences in trans- 
piration rates, and this should be obviated. 
The leaves in the potometer work and the potted plants 
were sprayed or dusted liberally, and in the case of the sprays, 
in partieular, care was taken to cover completely with a fine 
spray of the material both surfaces of the leaves. Тһе dust 
applications were made in the late afternoon when the leaf 
surfaces were less dry, and after dusting the upper surfaces 
of the leaves the plants were inverted and the lower surfaces 
equally well treated. Тһе dusts were prepared by grinding 
to an impalpable powder in а mortar. 
Тһе Bordeaux mixture employed was made by the 4-6-50 
formula, the weights of ingredients for making small quantities 
being approximately as follows: 
CuSO, 9.6 grams 
CaO 14.4 grams 
Water 1000 cc. 
The weak Bordeaux was one-half the strength of the above. 
The Са(ОН); was prepared by slaking gradually 60 grams of 
