544 Richards . — The Respiration of 
increased respiration. Experiments 8, 21 a, and 39 illustrate 
this point. 
The employment of well-aerated tissues, which, either from 
their small size or looseness of structure, afford free access of 
oxygen to their parts, threw yet more light on the subject. 
As has already been mentioned, seedlings of Vicia Faba , in 
spite of the irregularities in respiration associated with their 
rapid growth, showed an increase of C 0 2 upon injury. But 
better still for this purpose are leaves, of which, as will be 
seen, a number of different kinds were tried. In all cases 
there was a distinct increase, the maximum being reached 
a few hours after, or at least during the same day as, the 
injury ; while by the next day, if the leaf still lived, the 
respiration returned to about the normal (Expts. 28 and 32). 
It will be noted in all the experiments, both with seedlings 
and with leaves, that there was no sudden increase during the 
first few hours after wounding. It is, then, apparent that 
the shock of the injury itself must also play a part in the 
rise of the respiration of injured plants, since these parts of 
plants, which are already well supplied with 0 2 , or from their 
nature cannot contain any considerable quantity of oxidizable 
substances, also react when wounded. 
As regards the sudden evolution of C 0 2 that is noticed 
immediately after injury, the numerous experiments which 
were made to clear up this point seem to show that the 
phenomenon is due to the escape of this gas, already ab- 
sorbed or held in the tissue, in a physical rather than a 
chemical manner. As has already been stated, thin and 
loosely constructed tissues, and also small masses of a more 
compact nature, such as the hypocotyls of seedlings, showed 
no evidence of this temporary increase. It was only with 
bulkier tissues like potatoes and carrots where this was 
found : in tissues, that is, where their size made it possible that 
C 0 2 might be contained in them. But this point is more 
conclusively demonstrated in Experiments 12 and 19, in 
which the plants were exposed to a vacuum at once after 
injury. If there were any C 0 2 present, as such, in the tissue, 
