Wounded Plants. 
543 
was noted, which, however, increased very suddenly on re- 
moval of the binding, at which time the cuts gaped widely 
open and so allowed free access of air to the injured parts. 
These experiments show that there can be hardly a doubt 
that the oxygen of the air plays an important part in the 
reaction of the respiratory functions of the plant towards 
injury. 
Experiments made in atmospheres of hydrogen or of 
diminished percentage of oxygen substantiated those already 
described, and also showed some other facts. In Experiment 
1 1 it will be seen that even in 6°/ o oxygen the potatoes ceased 
to show the ordinary increase, but when finally exposed to 
air there was a gradual rising of the respiration-curve. In 
other experiments the percentage of 0 2 was reduced to as 
low as four, which Stich 1 has shown may be safely used 
without complicating the results with intramolecular respira- 
tion. The decrease shown in Experiments n and 21 after 
exposure to an atmosphere of this composition for six hours 
is not the normal decrease due to the healing of the wounds, 
as the considerable increase after remaining over night in 
a current of air demonstrates. Corresponding experiments 
were made with carrots, but, although much the same pheno- 
mena were noted, they were not quite so clearly marked as 
in the former cases. In pure hydrogen it is shown that the 
intramolecular respiration is not so largely increased by 
injury (Expts. 9 and 10). After nine hours’ exposure to 
hydrogen, the amount of C 0 2 evolved was scarcely greater 
than the normal intramolecular respiration. In considering 
these experiments one must always remember the necessary 
accommodation which the functions of the plant have to 
undergo to the diminished pressure of the artificial atmo- 
sphere. On the other hand, it is shown by the experiments 
carried on with pure oxygen that a surplus of this gas 
produces no effect in yet further increasing the production of 
C 0 2 , from which fact it would seem that simply the action 
of oxygen on the tissues is not alone responsible for the 
1 1. c., p. II. 
