1914] ’ HASSELBRING—EFFECT OF SHADING 269 
disadvantageous, since the cups were thus probably exposed to 
nearly the same average conditions of light and shade as the leaves. 
The record of evaporation from the cups during the course of the 
experiments is given in table V. The figures are all reduced to 
terms of evaporation from a standard atmometer whose coefficient 
is taken as unity. They are directly comparable, therefore, with 
each other and with the figures given by Livincston’ and by 
CALDWELL. 
Table V shows that the rate of evaporation is constantly less 
under the cheese-cloth cover than it is in the open. As with the 
relative humidity, the difference between the two stations increases 
with the development of the plants. During the early part of the 
period covered by the experiments, the cups in the open lost one- 
fourth to one-third more water than those in the shade, but later 
the loss from the cups in the open was more than twice that from 
those in the shade. The increasing divergence of the rates of 
€vaporation corresponds with the increasing quantity of water 
vapor given off by the growing plants. 
Rainfall 
As a rule, there is very little rainfall in Western Cuba in the 
winter months, during which the tobacco crop is grown, conse- 
quently tobacco and other crops grown during that season require 
Itrigation. The season during which this experiment was conducted 
Was no exception. The only rather heavy rains occurred on Decem- 
ber 13 and December 1 5, and on January 5. The complete record 
of rainfall taken from the weather observations at the station during 
e time of the experiment is as follows: 
December 2..__. 3.30 mm. January 1..-..- 1.02 mm 
. Soe: ae eb, ee a ee Ge 
ey CEO a ea as eames eae y oo an 
‘ | eee 37 «“ eg 12.88 “ 
ea se a es ee ee: 
3 Bl eccks $050 5 ne i Opener ae 
: *Livincston, B. E., A study of the relation between summer evaporation 
intensity and centers of plant distribution in the United States. Plant World 
34: 205-222. rorr, 
8 Be 
CaLpwett, J. S., The relation of environmental conditions to the phenomena 
of permanent wilting in plants. Physiol. Researches 1:1-56. 1913- 
