290 Plant Physiology 



man, and this fact is significant with respect to the im- 

 portance of these organisms in the general disintegration 

 of organic materials. 



167. Respiration of wounded plants. - - It has been re- 

 peatedly demonstrated that the respiratory activity is 

 increased by injuries to the tissues. Precise data upon this 

 point have been contributed by Richards. He employed 

 chiefly potato tubers, but the experiments with these tis- 

 sues were supplemented by carrot roots, also certain seed- 

 lings, leaves, and willow-twigs. In general, it is found 

 that following injury there is increased respiration for a 

 time. Usually after two days - - under the conditions of 

 the experiments - - the activity again declines to a rate 

 more nearly the normal. The chart (Fig. 71) shows the 

 C02 developed from the respiration of 24 small potato 

 tubers (weighing 200 grams) before and after wounding, 

 the wounding consisting of slicing the potatoes length- 

 wise. 



The ordinates represent milligrams of CO 2 , and the 

 abscissae, time intervals of one hour each, on parts of 

 several succeeding days as indicated. The sudden rise 

 in C02 production after the injury of such solid tissues is 

 explained by the inclusion of C0 2 , which is then rapidly 

 lost during the first two or three hours. 



168. Heat release. - - Exact determinations of the heat 

 release in plant respiration have not been possible with 

 the experiments as generally conducted. It has long 

 been shown, however, that the temperature inside of the 

 respiration chamber containing germinating seeds, open- 

 ing flower-buds, and other materials exhibiting vigorous 

 respiration maybe 5 or 10 C. above that of the surrounding 



