400 BOTANICAL GAZETTE [JUNE 
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horsechestnut bulb; ........... naked bulb. Abscissas represent 
FIG. 7; 
5° F.; ordinates, 100 seconds. See Table II. 
The first column of figures represents the readings in degrees 
from the thermometer with the naked bulb; the second column 
the same from the bud-covered instrument; the third column shows 
the time in seconds from the beginning of the experiment; the 
fourth column the difference in degrees at each reading; and the 
fifth column is the ‘“time-difference,” so-called, which represents 
the number of seconds elapsing after a reading on the naked bulb 
before the same temperature was reached on the horsechestnut 
bulb, in other words, the number of seconds by which the bud- 
scales retarded the fall of temperature in the enclosed bulb. 
While not attempting to deduce the physical laws governing 
the fall of temperature in each case, we may note from the tables 
and curves several points which bear upon our problem. It will be 
seen that theoretically the time required for the temperature to fall 
in either case is infinitely long, the curve becoming nearly horizontal 
towards the end of each experiment. But for all practical pur- 
poses, and as closely as my instruments would measure, the fall 
was completed in about thirty minutes in each case. The greater 
part of it, in fact, was completed in ten minutes. As regards time, 
in Table II the very much more rapid radiation of heat more than 
balanced the effect of the greater quantity of heat to be radiated. 
As we should expect, the retarding effect of the bud-scales in 
degrees, shown in the fourth column, was much greater in case 
of the greater extremes of temperature, and was greatest when the 
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