STIMULATION 115 



and generally also by a rise in temperature. The intensifica- 

 tion 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 demon- 

 strated 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. There 

 is an initial outburst of carbon dioxide, followed by a fall, a 

 feature not at all uncommon after drastic stimulation, and 

 the absorption of oxygen is rather greater than the amount 

 theoretically required for the quantity of carbon dioxide 

 evolved. Richards considers 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. 



In the potato, Hopkins f demonstrated an increase in the 

 sugar content of the tuber after wounding, it gradually rises 

 to a maximum and then falls. He considers that the increased 

 intensity of the respiration is explained, at any rate in part, 

 by the increase in the sugar content. 



Muller J investigated the respiration of trees after lopping, 

 and found a seasonal variation in the traumatic reaction : 

 the reaction of Picea is about the same all the year round, 

 whilst Fagus and Fraxinus show the greatest reaction in 

 spring and autumn, and the least in summer, as estimated 

 by the output of carbon dioxide at the mean temperature 

 of the month. 



White § found that pollination produces a rapid increase in 

 respiratory activity and affects the C0 2 /0 2 ratio which generally 



* Richards : " Ann. Bot.," 1897, II, 29. 



f Hopkins : " Bot. Gaz.," 1927, 84, 75. 



I Muller : " Dansk. Botanisk Ark.," 1924, 4, I. 



§ White : " Ann. Bot.," 1907, 21, 487. 



