July 7, 1923 
Temperature Effects in Plant Metabolism 
17 
C. the evaporation value for any relative humidity below 100 per cent 
would bear the ratio 18.2:12.2 or 149:100. Hence, evaporation should 
be 49 per cent greater at the higher temperature than at the lower one. 
In the case of die black atmometers, which correspond more closely to 
plants than do the white ones as regards water loss when illuminated, 
it appears that the tendency to transpiration was about 31 per cent 
greater in the warmer house than in the cooler one. As will appear 
subsequently, this lesser difference of the black as compared with the 
white instruments is probably due to greater duration of sunlight in the 
cooler house. 
Considering the increase of evaporation from the black atmometer 
over that from the white one as an index of the exposure to sunlight, it 
appears that the latter was appreciably greater in the cooler house 
than in the warmer one. This difference is probably due to the fact 
that the former house was on the western and the latter on the eastern 
side of a group of four parallel ranges of greenhouses. As a result, the 
cooler house received direct sunlight for a greater part of the day than 
the warmer one. The atmometric data indicate that the solar radiation 
was about 44 per cent greater in the former case. 
The only significant difference in chemical composition between the 
plants grown at the two temperature ranges resides in the acid-hydrolyzable 
carbohydrates or polysaccharids. These compounds are included in the 
group of roughly defined hemicelluloses. There is no overlapping of the 
values for individual cultures at the different temperatures in this case, 
and the average value of the reducing sugars formed is about 4 per cent 
greater at the lower than at the higher temperature. Thus, a combina¬ 
tion of relatively greater illumination, lower saturation deficit of the 
atmosphere, and lower atmospheric temperature was accompanied by 
increased storage of carbohydrates in the clover plant. 
BUCKWHEAT (POLYGONUM FAGOPYRUM) IN SOII, CULTURES WITHIN CLI¬ 
MATIC chambers 
In view of the desirability of conducting plant cultures with variation 
of only one climatic factor, while limiting the others to as constant 
values as practicable, special chambers were constructed for this purpose. 
These were placed in the southern end of the greenhouse previously used 
for the higher temperature range. A section about 8 feet long at this 
end of the house was separated from the main portion by a partition of 
artificial boarding. The southern side of this partition was painted 
glossy white so as to reflect light into the climatic chambers which stood 
close by on the ends of the usual greenhouse benches. It was necessary 
to exclude sunshine from the culture chambers, for the radiation effects 
otherwise produced were uncontrollable. For this purpose curtains of 
bleached muslin were suspended from the ridge to the gutters of the 
greenhouse compartment and on the end of the house. These were 
pushed aside on cloudy days. 
Plate 1, A, shows the climatic chambers in operation, together with por¬ 
tions of the humidifiers. The general arrangement consisted of humidi¬ 
fying chambers in which the minimum possible temperature imparted 
to the conditioned air current was limited by the temperature of the 
water supply from Lake Mendota. 
As used, the temperature of the water was raised by electric heaters 
with thermostatic controls. On leaving the humidifier the air passed 
48107—23 - 2 
