Wounded Plants . 
537 
regarded, being a scarcely perceptible fraction of one per cent. 
In all cases the percentage of 0 2 in air was taken as 20-8, 
being the average amount shown by repeated analyses with 
this apparatus, and agreeing well enough with the already 
known percentage. 
For certain determinations of the amount of C0 2 contained 
in thick bulky tissues such as potatoes, carrots, &c., a method 
was employed for driving the gas off with boiling water. 
A large flask, in which the potatoes or carrots were placed 
along with a considerable amount of water, was connected by 
means of a Liebig-condenser in reversed position with the 
Pettenkofer apparatus. The water was brought to the boiling- 
point as rapidly as possible, care being taken that no gas 
could escape from the flask, except through the tubes con- 
taining the Ba0 2 H 2 , and also that no water passed over from 
the condenser into the tubes. The C0 2 evolved was estimated 
in the usual way by titrating the remaining Ba0 2 H 2 . Almost 
all of the C0 2 thus driven off came over in the first ten 
minutes after boiling. The method is open to the objection 
that the high temperature required might bring about the 
decomposition of organic substances in the tissue, and thus 
give an excess of C0 2 ; but the fact that the gas comes off so 
suddenly would seem to point to its being merely absorbed or 
enclosed. The results were only accepted as approximate at 
best, and, as will be seen, no very great stress is laid on them. 
All the material experimented with, with the exception 
of the leaves from the green-houses, was brought into the 
laboratory at least four days before using, to allow it to 
become accustomed to the temperature of the room. In 
almost all cases the respiration of the uninjured condition 
was first ascertained, the only exceptions being a few cases 
with potatoes, in which it was known that the respiration was 
practically none from experiments made previously with 
similar potatoes. The character of the plants and tissues 
employed for experimentation was various : bulky tissues 
like potato-tubers ( Solanum tuberosum ), carrots ( D aliens 
Carota ), &c. ; thin, well-aerated tissues such as various leaves ; 
o o 
