Wounded Plants. 
545 
it would naturally come off under the reduced pressure, and 
such was found to have been the case : for, although de- 
terminations were made but half an hour after injury, the 
sudden increase and subsequent fall found under ordinary 
atmospheric pressure were not observed. When injured 
potatoes are transferred to hydrogen, there is at first a con- 
siderably greater evolution of C 0 2 than some hours later ; 
which, as Stich has pointed out, is due to a process of ac- 
commodation which the plant undergoes, but which may also 
partly be due to the cause mentioned above. In the relation 
of the C 0 2 produced and 0 9 absorbed during the first few 
hours after injury, further support is found for the opinion 
here expressed regarding the source of the excess of C 0 2 . 
It will be seen that, whilst the C 0 2 - production is very large, 
the absorption of 0 2 during the first two hours is less than 
later, when the C 0 2 evolved has greatly decreased. Reference 
to Experiment 37 will show this, where with potatoes the 
amount of C 0 2 given off during the first two hours after 
injury was 2*19°/, of the air in the receiver, while but 2°/ o of 
0 2 had been absorbed. Further, during the next two hours 
i* 83°/ 0 of C 0 2 was evolved to 2*5°/ 0 of 0 2 absorbed ; whereas 
on the next day, when the C 0 2 - production was again above 
2°/ o , the figures stood : C 0 2 produced 2*56°/ o ; 0 2 absorbed 
3‘2°/ 0 . In the experiments with carrots the same result was 
also obtained ; first two hours, C 0 2 3-71% to 0 2 3*8o°/ o ; 
second two hours, C 0 2 2*35°/ o to 0 2 y 6 °/ o ; third two hours, 
C 0 . 2 3.7% to 0 2 5-3% (Expt. 4). 
To obtain some idea of the amount of C 0 2 which may be 
contained in such a large mass of tissue as a potato or a 
carrot, a number of experiments were made by which the 
contained gas was driven off by boiling water. The amount 
of C 0 2 thus obtained was about 5 mg. to every gram of 
substance (Expts. A — G). The method is open to the 
obj ection that perhaps some of the C 0 2 driven off may have 
been formed by the decomposition by the heat of organic 
compounds in the plant ; but without much doubt a large 
portion of the gas was simply the contained or absorbed C 0 2 
