84 BOTANICAL GAZETTE [FEBRUARY 
generally speaking, prevent the stomata showing normal behavior, 
e. g.,in closing at night, or by artificial darkness during the day, 
or again when the petiole is divided and the leaf begins to wither. 
The purely physical results of the warmth of the bulbs have 
also to be considered. Supposing the apparatus is in equilibrium, 
and the pen therefore is running along the zero line, indicating 
equality of temperature in the bulbs; if a bad conductor, such 
as a flock of cotton wool be placed on one bulb, the pen will 
instantly be deflected, as shown at 8:25 P. M., fig. T. 
EXPERIMENT 83 B, fig. z. /uly 2, 1900, COTTON WOOL. 
Pp, M. 
6:36-8:20 Nothing on either bulb. 
- The battery turned off, and a thick pad of cotton wool placed on 
bulb B; this prevents loss of heat from B, and therefore gives 
an R-coolS movement when the battery was turned on. 
Battery on: result, an R-cool rise of about 1.7° C. 
10:2 Wool removed: result, an R-warm fall. 
8:25 
In the same way, if a good conductor, e. g., a thin metal plate 
or a withered leaf, is placed on bulb R, the result shown at 5:56 
in fig. 2 will be seen; the effect of its removal is seen at 8:28. 
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It is clear that these facts must be taken into account in experi- 
ments on leaves. This difference in temperature would not in 
3The two bulbs of the thermometer are distinguished as bulb B and bulb R. 
When the pen is deflected from the zero line it — a pee of temperature 
between B and R which may be called a “B-warm” or cool” effect; while # 
ontrary effect would be described as either “B-cool” or the Spaaivaieat “ R-warm: : 
