Curtis : SoME OBSERVATIONS ON TRANSPIRATION 367 
moisture. The temperature would remain constant for long 
periods but the humidity was subject to more considerable varia- 
tions. I was interested to observe what results would follow 
changes of humidity, A rise of a few per cent. had no effect 
that could with certainty be recognized. The following figures 
will illustrate the result when the humidity was changed at 11 
o'clock from 36 to 44. 
III. Errectr or Moisrure 
Io A. M. Ir 12 t 2 Temp. Hygrm. Time. 
Aucuba Japonica, 167 164 136 167 108 18.5 <i Bae 
Richardia Africana, 142 138 135 siz. 206 36 ot 
Opuntia camnessa, 5 7 o 4 3 44 12 
Begonia metalica, 98 117 93 80 7o 8:19 44 I 
Cycas revoluta, 70 7O 37 29 20 44 . 
The result of this very considerable change is unmistakable 
and is apparent in the increased irregularities of the curve. The 
Variation in Opuntia is in keeping with what might be expected 
from a plant of so pronounced adaptive character. It should be 
Stated, however, that the curves of several cacti, obtained under fairly 
uniform conditions, were very uneven. These results are such as 
to warrant the conclusion that no serious error was being intro- 
duced through the fluctuations of the hmidity. 
A few measurements are given in Table IV., of the transpiration 
of plants in the dark. Occasionally there is apparent a rhythm 
Corresponding to the daily periodicity, but on the other hand it 
not unfrequently happens that there may be an irregular decline 
from the start or the curve may be characterized by a rise or fall 
without reference to the period of the day. I have noticed on 
Several occasions that pronounced maxima may be found early 
in the morning—between 5 and g o'clock. 
Manifestly little importance is to be attached to the results ob- 
tained under such conditions inasmuch as they represent the work 
performed under practically pathological conditions and the results 
throw little light upon the real action of the plant. While the rate 
becomes more uniform as Kohl and Wiesner have pointed out there 
'S also to be noted a marked decline and the plant is less responsive 
to the stimuli of light, all the phenomena, in fact, point to a cessation 
of the activities. The tissues become congested and it is apparent 
