64 PLANT RESPIRATION 



Thus it is evident that in pea seeds alcohohc fermentation 

 appears as a normal germination process which is induced by 

 a temporarily anaerobic mode of life. Devaux^ has shown that 

 a deficiency of oxygen often exists in the interior of the woody 

 cylinder of trees and anaerobic respiration then sets in. This 

 investigator proved that in wood parenchyma an accumulation 

 of alcohol takes place under some circumstances. Gerber- 

 claims that alcoholic fermentation never fails to appear during 

 the ripening of various fleshy fruits and that the process is 

 related to the formation of various esters which are to be 

 regarded as normal constituents of the given fruits. In fact it 

 is not unlikely that a deficiency of oxygen makes itself felt in the 

 ripening of various fruits. The results of Boysen- Jensen^ 

 allow it to be supposed that for grapes the absorption of oxygen 

 is only slight. This is also easily understood, since the skin 

 of the grape is but slightly permeable to oxygen. 



On the other hand we are justified in claiming that various 

 plants and plant organs, such as the foliage leaves of most trees, 

 never experience a lack of oxygen, since they live continually 

 under conditions of excellent aeration. The situation is the 

 more noticeable that these parts are also qualified to respire 

 anaerobically and to form alcohol in the absence of oxygen. In 

 their review of the physiological significance of anaerobic 

 respiration, various investigators have assumed that this proc- 

 ess represents a biological adaptation. The immediate death 

 of the plant is thought to be prevented by means of anaerobic 

 respiration in the case of an occasional deprivation of oxygen. 

 This conception must be rejected as insufficient and too weak to 

 hold. Apart from the consideration that biological- teleological 

 ways of thinking are in general insufficient for biochemical 

 questions, the supposition is in itself scarcely plausible that a 

 physiological process could appear only incidentally as a pre- 

 cautionary measure. Indeed we know that anaerobic respira- 

 tion is universally widespread. So far there has not been found 

 a single plant which is unable to form CO2 in the absence of 



' Devaux. Compt. rend. 128: 1346. 1899. 



• Gerber. Ann. sci. nat. bot. 4: i. 1896. 



' Boysen-Jensen, P. Det. kgl. danske videnskab. selskab. biol. meddel. 4: i. 1923. 



