ais Curtis : SOME OBSERVATIONS ON TRANSPIRATION 
under exceptionally brutal conditions. Devices which employ 
shoots or portions of the plant are of great value for demonstra- 
tions rather than as a means for the exact determination of 
actual processes. This remark may also apply to the measure- 
ments obtained by condensation or absorption of vapor. Work 
conducted under so artificial and unusual conditions can only give 
uncertain results. 
SUMMARY 
On cloudy and stormy days when the intensity of the light is 
quite uniform or at least not in keeping with the time of day, the 
transpiration curve shows a pronounced maximum near midday 
and it is also characterized by minor fluctuations that occur inde- 
pendently of climatic changes. 
An illumination of an electric light of goo candle-power under 
uniform external conditions demonstrated a periodicity in the trans- 
piration of several plants that corresponds in the main with the 
curves determined on cloudy days. The harmonizing of the 
rhythms of absorption, exudation and tension of fluids and the rate 
of growth is suggestive of the vital character of transpiration. 
Variations of a few per cent, in the humidity of the atmosphere 
produced no change in the amount of transpiration that could be 
determined with certainty. An increase of 8 per cent. resulted in 
a marked drop in the rate. : 
The curve in the dark sometimes was in keeping with the 
rhythm found under constant illumination but more frequently It - 
characterized by variations quite out of keeping with the periodicity 
of light. There is evidently a cessation of the vital action of the 
plant and the retarding of the rate together with its more gp 
nounced regularity is in keeping with the loss of tone manifest 
the plant. 
The very considerable volume transpired in the dark indicates 
that the stomata may be sufficiently open to allow the escape : 
vapor. This may be brought about in connection with the inter ; 
change of the gases in respiration or possibly by the independen 
action of certain stomata that are especially affected by the = 
creased turgor tensions or vapor tensions of intercellular transpita- 
tion. Only in the case of Cycas revoluta did the amount of trans 
piration appear in keeping with the ratios determined for cule 
transpiration. 
