the Respiratory Exchanges of Leaves. 703 
which there is no recovery, for it is always quickly followed by the condition 
of complete disorganization associated with the chocolate colour. 1 
Experiment IV. July 14, 1909. Dose, 0*5 c.c. for twenty minutes. 
Temperature, i8*4-i8*7°C. Fresh leaves. The leaves were of the current 
season, and were cut a few hours before they were used. 
The absorption of oxygen proceeded much more quickly during the 
first half-hour after treatment with chloroform, but rapidly diminished to 
a low level, from which it slowly sank through a period of thirty-six hours. 
The C(X output, on the other hand, had fallen even in the first half-hour to 
a very low level, and fourteen hours later was inappreciable. 
HOURS AFTER CHLOROFORM 
Fig. 5. 
Experiment V. July 10, 1909. Dose, 0-5 c.c. for fifteen minutes. 
Temperature, 14-15 0 C. Starved leaves. 
The leaves had been in the dark for several weeks, and were yellow to 
the extent of about a third of their area. Here the 0 2 intake was still 
more markedly increased. In fact, during the first half-hour, the six leaves 
had absorbed together more than 3 c.c. of oxygen. This rapid absorption 
of oxygen is still more striking when compared with the low rate of 
respiration previous to chloroforming. It is to be correlated with the 
change of colour to chocolate, due to the oxidation of substances of the 
nature of tannins under the influence of oxidases. 
In both these experiments it is probable that much oxygen had already 
been absorbed in the chloroforming vessel. This applies especially to 
Experiment IV, where the fresh leaves would still have their stomata 
open, and so present little resistance to the inrush of oxygen, which is the 
probable explanation of the lower rate of absorption detected in this experi- 
ment. In both, the rate of absorption appeared already to be rapidly 
diminishing. This point was studied further in the case of Helianthus. 
1 If the first symptom appears locally, the rapid complete disorganization is similarly localized, 
and only spreads slowly to neighbouring parts of the leaf. 
