1914] HASSELBRING—EFFECT OF SHADING 259 
order to determine the effect of the cheese-cloth on the environment 
of the plants, measurements were made during the course of the 
experiments of the various environmental factors both under the 
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Fic. 1.—Photograph of the cheese-cloth used in the experiments; natural size 
cheese-cloth and in the open. The results of these measurements 
are given in the following paragraphs. 
LIGHT 
The light intensity under the two conditions was measured by 
the Photometric method. The method in general was that de- 
scribed by Wiesner? and used by him in his extensive researches 
on the light relations of plants. However, owing to the difficulty of 
making a sensitive paper which at some stage in the process of dark- 
ening would exactly match the normal tint kindly sent the writer 
by Professor W IESNER, a standard instrument, the Wynne exposure- 
meter, was used in these observations. The time of exposure was 
measured by means of a stop-watch. The applicability of this 
method, as well as its shortcomings, have been fully discussed 
by Wiesner and others, and recently Lrvuvcston‘ has subjected 
* Wiesner, J., Der Lichtgenuss der Pflanzen. pp. 10-33. 1907. 
' Livixcston, loc. cit. 
