Wounded Plants . 
55i 
That there are yet other forms of irritation to which plants 
respond by increased activity goes without saying. The 
familiar examples of the effect of many plant-parasites on 
their hosts show that this may become evident from even 
a morphological standpoint ; and in other cases, where no 
direct atrophy or hypertrophy results, it would no doubt be 
found that the host-plant endeavours to counteract the effect 
of the parasite in such a way. Bohm 1 mentions the fact that 
the respiration of potatoes affected with Phytophthora is above 
the normal. Of course in such cases the period of stimulation 
is more prolonged than by simple wounding, for the source 
of irritation is always present, and also increasing ; but before 
the plant succumbs there must be a time when the effect of 
the stimulus given by the parasite has reached a maximum. 
Different as they may be, these examples all serve to illus- 
trate the power of reaction against untoward and abnormal 
conditions which plants possess in common with other living 
organisms. 
Statement of Conclusions. 
To recapitulate in brief the conclusions arrived at from the 
experiments here recorded, as far as they can be judged from 
the plants employed, they may be stated as follows 
1 . That after injury to plant-tissue there results a greatly 
increased respiration, varying in intensity and duration with 
the character of the tissue involved and with the extent of the 
wounding. This increased activity of respiration, after reaching 
— usually within two days — a maximum, falls gradually, as the 
wounds heal over, to a normal or to an almost normal rate. 
2. That this increased respiration may be ascribed to an 
effort on the part of the plant to recover from the injury by 
which the ordinary functions of the plant are stimulated, 
thereby demanding and necessitating an increased supply 
of oxygen. 
Bot. Centralblatt, Bd. 1 , p. 202, 1892. 
x 
