566 RESPIRATION AND FERMENTATION 



The traumatic stimulus extends only to a certain distance from the 

 incision, and hence the greatest total effect is produced when a potato 

 or leaf is cut into a number of pieces, for the respiratory activity subse- 

 quently attains the highest possible maximum. A rise of temperature 

 accompanies the increased respiratory activity, and by means of thermo- 

 electric measurements Richards has shown that this ceases to be perceptible 

 in a potato at about 2 centimetres from the injured surface. The rise of 

 temperature is, however, only slightly less marked at this distance in the bulb 

 of Allium cepa, and other facts show that the reaction due to the wound 

 spreads over the entire bulb. 



In the absence of oxygen no such reaction is possible in aerobic plants, 

 but an increased intramolecular-respiration is exhibited if the air is replaced 

 by hydrogen after the reaction has commenced. When the primary reaction 

 due to the injury has passed away, the production of carbon dioxide may 

 fall below its original value, owing to the depressed vital activity of the 

 separated parts ; this was observed to be the case by Ad. Mayer and 

 Wolkoff * in isolated portions of seedlings, and by Borodin 2 in cut branches. 

 On the other hand, respiration may undergo a permanent increase when an 

 injury leads to the formation of new shoots or roots. Bohm 3 has shown 

 that a potato attacked by Phytophthora respires more actively, and it is 

 probable that similar phenomena accompany the formation of galls by 

 fungi or insects. 



SECTION 105. The Importance of Respiration. 



A continual supply of energy is necessary for the maintenance of 

 vital activity (Sects. 77 and 94), and hence the possibility of aerobic or 

 anaerobic respiration is a primary essential for all vital processes, including 

 those which do not involve any direct consumption of kinetic energy. 

 Functions of this kind are more open to investigation than the funda- 

 mental vital processes which proceed in intimate connexion with aerobic 

 or anaerobic respiration. It is still uncertain whether the katabolic 

 processes by which energy is liberated take place outside the living pro- 

 toplasmic elements, or involve a continual destruction and regeneration of 

 the latter (Sect. 101). Still less is known as to the manner in which the 

 energy thus liberated is made available for the maintenance of vital activity, 



1 Landw. Jahrb., 1874, Bd. in, pp. 501, 533. 



9 Borodin, Bot. Jahresb., 1876, p. 922. Muller-Thurgau observed a decrease in the respiration 

 of potato-tubers when separated from the parent plant (Landw. Jahrb., 1885, p. 857). A similar 

 example of the same phenomenon was also observed by Ewart (On Assim. Inhib., Joum. of Linn. 

 Soc., 1896, Vol. xxxin, p. 392) on thawing branches injured by frost. 



3 Bohm, Verb. d. Zool.-Bot. Ges. in Wien, 1892, Bd> XLII, p. 47. [This increase must not be 

 confounded with that due to the presence of the living and respiring fungus, and any agency which 

 suffices to kill or remove the fungus may act as a stimulus exciting an increased respiratory activity 

 in the potato.] 



