88 BOTANICAL GAZETTE [FEBRUARY 
between their temperatures, as seen on the curve, should have 
diminished by 53™™. As a fact it only diminished by 14™*, 
#7. e., the effect as measured by the Callendar recorder is only 
26.4 per cent. of the actual change. Between 4:19% and 5:11 
the difference between wet and dry bulbs increased (as the air 
grew drier again) from 0.8° to 2.1°,2.¢., by 1.3°C. This should 
have given a change on the recorder-curve of 317". The 
recorded change was not at any rate more than 8™", 7. ¢., 25.8 
per cent. of the actual psychrometer effect. 
EXPERIMENT 108. March 16, r90r. NARCISSUS. 
In this experiment the effect of damp air is shown with a Narcissus leaf 
on bulb R and with nothing on bulb B. The floor and hot pipes were watered, 
with the following result: 
P.M, Dry, °C. Wet, “C. Per cent. 
2iit - - 17.9 _ 52 
Watered floor and pipes. 
ey ee - 18. 16.8 85 
2257 - - 18.2 172 go 
2:56 - - - Opened door. 
3:1 ‘ - 16.8 13.5 67 
Thus, between 2:11 and 2:27, the difference between the wet 
and dry bulb mercury thermometers decreased from 5.2° to 1.0°, 
z.@., by 4.2°. This would mean a fall in the curve of 100.8", 
The actual change in the curve was a drop of 22™", or in round 
numbers 22 per cent. of the psychrometer difference. The sto- 
mata were wide open throughout the experiment. Between 2:27 
and 3:2 the difference between wet and dry mercury thermome- 
ters increased by 1.7°, which would equal 41™"; the change in 
the curve was 12™™", or 29 per cent. of 41™™, 
It should be added when an ordinary thermometer is con- 
verted into a wet bulb by Wrapping it in a leaf, the difference 
between it and a dry bulb is considerably less than that between 
the wet and dry bulbs of a psychrometer.7 
It is not obvious why the leaf when wrapped around the bulb 
of a thermometer behaves so differently from the wet gauze with 
which the psychrometer is covered. But the cause, whatever it 
7 DARWIN, FRANCIS, Observations on stomata. Phil. Trans. Roy. Soc. London. B. 
190; 583. 1898. 
