320 
Journal of Agricultural Research voi. xxm, no. 5 
shows the temperature for a number of hours within folded blotters near 
the middle of trays 1,2, and 6, and also the temperature indicated by 
the thermometer in the top of the chamber. The effect is that of broad¬ 
ening the curves and displacing them to the left as viewed downward 
from the top tray. 
Three of the eleven alternations were secured by transferring the seed 
trays with the seeds upon them between two germination chambers con¬ 
stantly maintained at fixed temperatures. In this case the temperature 
changes taken altogether were more nearly identical in different parts of 
the chambers, and approximate equilibrium in temperature between the 
different parts of the chambers was assumed much more quickly than in 
the two types of alternations previously discussed. Figure 15 shows 
the temperature changes within wet plotters near the middle of trays 2 
and 6 in such an alternation. 
Figure 16 shows much more rapid cooling of the air in the top of a 
chamber which is being cooled by ice and cold water above than within 
the blotters on the seed tray just below this layer of air. Such differ¬ 
ences as here shown might be significant in determining whether, in a 
given case, a given kind of seed, for instance celery, will germinate better 
between blotters or on top of blotters. 
COMPARISON OF THE DIFFERENT TEMPERATURE ALTERNATIONS 
While the differences in the progress of temperature changes between 
different parts of a given chamber were frequently large, they were 
always less than the differences in the same part of different chambers 
which were used for different alternations. For the purpose of com¬ 
paring the temperature changes in the different alternations, a position 
near the center of tray 6 was selected. Figure 17 shows the time- 
temperature curves for this position in all 11 alternations, which are 
numbered from 1 to 11 for convenience. The curves were drawn from 
actual observations for the first 15 hours and were projected for the 
remaining 9 hours of the day. Since the initial temperature varied in 
each case a few tenths of i° C. from day to day but was always very 
near 20°, the curves have been slightly rectified so as to begin each at 
exactly 20°. 
Alternations No. 1 to 3 were obtained by transferring between two 
chambers at fixed temperatures; No. 4 to 6, 8, and 10 by heating and 
then immediately cooling a single chamber; No. 7 and 9, by heating a 
chamber and then holding it for three hours at the highest temperature 
reached before beginning to cool it; No. 11 was obtained by heating a 
chamber and then allowing the temperature to fall naturally, without 
artificial cooling. The rates of heating and cooling were approximately 
the same from day to day in any one alternation. In all alternations 
after the temperature had fallen to 20° C. it was held nearly constant 
until heating was begun the next day. 
The alternations differed widely in maximum temperature attained, 
mean daily temperature, and rate of cooling; but the heating was relatively 
rapid in all cases and the minimum temperature was the same in all cases. 
