270 BOTANICAL GAZETTE [APRIL 
Summary of observations on environment 
The data relating to the changes in the environment induced 
by the cheese-cloth shade may be briefly summed up here. 
The light intensity is greatly modified by the cheese-cloth shade. 
The total light under the cloth is reduced by about one-third, but 
the diffuse light inside the tent is only slightly reduced. It appears, 
therefore, that the plants inside the tent receive a smaller quantity. 
of total light than the plants outside, but an almost equal amount 
of diffuse light. 
The cheese-cloth tent shows very little effect on the temperature. 
On the whole, the temperature outside the tent is slightly higher 
than that inside. The average difference for the 60 days, however, 
is only about 0°14 F. This can have but little effect on the tran- 
spiration of the plants. It appears that any tendency of the tent 
to retain heat is compensated by the reduced amount of radiant 
energy which passes into the tent. 
The difference in the relative humidity of the two stations is 
much greater than the difference in temperature. This difference 
is restricted to the hours of sunlight, for at night the relative 
humidity in both stations reaches 100 per cent. During the day 
the difference is enhanced by the partial retention by the tent of 
the water transpired by the plant. 
The rate of physical evaporation is greater in the open than 
under the cheese-cloth shade. The divergence of the rates of 
evaporation in the two stations increases with the development of 
the plants and the consequent increase in relative humidity under 
the cheese-cloth. 
Aside from the lessening of the illumination and the increase in 
relative humidity, the cheese-cloth effects a reduction of air currents. 
All these changes tend to diminish transpiration. 
Materials and methods of experimentation 
The plants used in this work were grown from seed obtained 
during the previous season from a single self-fertilized mother- 
plant, whose offspring was shown by subsequent cultivation both 
in Cuba and in the United States to be of a pure strain? From 
* The strain used was the no. 7 described in the following paper: HASSELBRING, 
H., Types of Cuban tobacco. Bor. Gaz. 53:113-126. pls. 4-10. 1912. 
