78 RESPIRATION 



that the amount of heat liberated by germinating peas decreased 

 with age. 



Since respiration is a means of obtaining energy for the 

 needs of the plant, the evolution of heat represents excess of 

 energy and is a waste product, for which reason the temperature 

 of a normally respiring plant is not by itself a sure guide to the 

 amount or intensity of physiological combustion but rather a 

 measure of the inefficiency of the organism. 



STIMULATION. 



The stimulation of the plant accelerates respiration, which 

 acceleration is marked by a rise in the output of carbon 

 dioxide and generally also by a rise in temperature. This is 

 particularly true for the stimulus provided by wounding ; as 

 F. F. Blackman said on a certain occasion, " Precisely the 

 same effect is produced by peeling a potato as by flaying 

 a saint." This intensification of respiration resulting from 

 traumatic stimulation long has been known and now is not an 

 uncommon laboratory exercise. Richards* found a gradual 

 rise in temperature following the stimulus, attaining its 

 maximum about twenty-four hours after the infliction of the 

 injury. In massive tissues the effect is local, but in less 

 compact structures, an onion bulb for example, the rise in 

 temperature may be demonstrated over a more extensive 

 area. The rise may be two or three times as large as the 

 difference between the normal temperature of a potato and that 

 of the surrounding air. The precise increase in respiration 

 depends on the extent of the injury and the nature of the tissue 

 operated on. With regard to the output of carbon dioxide, 

 there is an initial outburst followed by a fall, a feature not at 

 all uncommon under drastic stimulation, and the absorption of 

 oxygen is rather greater than the amount theoretically required 

 for the quantity of carbon dioxide evolved. Richards con- 

 siders that the initial outburst of carbon dioxide in part is due 

 to the release of the gas normally enclosed within or absorbed 

 by the tissues, the " residual " carbon dioxide which normally 

 is not exhaled. 



With regard to other forms of stimulation, White f found 

 that pollination produces a rapid increase in respiratory activity 



* Richards : " Ann. Bot.," 1897, II, 29. f White : Id., 1907, 21, 487. 



