July 7, 1923 
Temperature Effects in Plant Metabolism 
19 
temperature difference between the two chambers of 5 0 , while practically 
equal saturation deficits were maintained in the two cases. A compari¬ 
son of saturation deficit with relative humidity is given by Livingston 
(25X The necessary computations are as follows : 
Temperature. 
Vapor pressure 
at saturation. 1 
Vapor pressure at relative 
humidity of— 
i ; 
Saturation def¬ 
icit (by differ¬ 
ence). 
70 per cent. 
| 78 per cent. 
C. 
Mm. 
Mm. 
Mm. 
Mm. 
17 ° 
J 4 - S 3 
IO. 17 
4 ' 3<5 
22° 
19.83 
15 - 47 
4 * 3 6 
1 The values in this column are from Fowle (6). 
As shown in Plate i, B, where the black spores are conspicuous, the towel¬ 
ing was badly affected by molds. Addition of copper sulphate to the 
water stream proved ineffective after the organisms were established. 
From the experience of Morse with the destruction of copper-ferrocyanid 
membranes by molds (28, p. 833 ) there would seem to be little hope of 
avoiding difficulty by impregnation of the toweling with insoluble com¬ 
pounds of toxic elements. We are therefore substituting spray nozzles 
for humidification in future operation. 
ILLUMINATION 
Guided by exposure tests with photographic paper, additional shading 
was provided for the more westerly chamber, so as to equalize the solar 
radiation received by the two series of cultures, as indicated by the water 
losses from the black atmometers. The diminution of light intensity 
incident to the necessary shading of the chambers was partially com¬ 
pensated by placing a 500-watt, Mazda C, electric lamp over each. 
These were sufficiently distant to avoid serious heating effects and the 
light was concentrated upon the plants by conical reflectors. They were 
operated daily from about 5.30 p. m. to 9.30 p. m. and throughout 
cloudy days. Typical measurements of light intensity at the approxi¬ 
mate level of the culture jars were obtained with a photometer. These 
appear in Table III. 
Table III. — Photometric values of light intensity in foot candles 
Location of test. 
Character of day. 
Isolated 
Within 
Within 
Shade of 
compartment 
climatic 
climatic 
main house. 
south of 
chamber. 
chamber, 
chambers. 
lamp off. 
lamp on. 
Clear... 
160 
90 
8S 
145 
Cloudy. 
40 
20 
IS 
SO 
The beneficial effect of the artificial illumination was apparent in the 
growth response of the plants. Distinct etiolation of the latter became 
evident during early growth and before the lamps were installed. 
With reference to the efficiency of the climatic apparatus as a whole, 
in view of the lack of refrigeration and other limitations it would be 
