88 PLANT RESPIRATION 



Detailed studies by these workers have estabhshed the fact that 

 the zymase of yeast is indifferent to atmospheric oxygen. Its 

 action is the same with access to oxygen as with the exclusion 

 of oxygen. Now the question is: why do seed-plants and other 

 aerobic organisms produce no alcohol under normal hving 

 conditions, and why does the action of zymase become con- 

 spicuous in them only when oxygen is excluded? Either the 

 zymase of seed-plants is not wholly identical with that of yeasts 

 or the products of the action of zymase disappear when exposed 

 to air as a result of the action of oxidation processes. The latter 

 assumption forms the most important basis of the theory of the 

 connection of anaerobic with normal respiration. 



Actually only the results of Diakonow's experiments could 

 be lined up against all the points which favor the theory of 

 connection, but it must be kept in mind that Diakonow himself 

 in a later paper declared that his earlier results were not wholly 

 rehable. For that reason it was necessary to repeat Diakonow's 

 work. 



This repetition was carried out by Kostychev^ and yielded a 



disproof and clarification of the most important results of 



Diakonow. The experiments were performed first in nitrogen 



in order to rule out the eventually injurious effect of hydrogen 



or its impurities. Pure cultures of the molds Aspergillus niger 



and Rhizopus nigricans were grown on solutions of grape sugar, 



quinic acid, peptone and tartaric acid. Cultures fed with either 



sugars or non-sugars gave off CO2 in the absence of oxygen. 



Later it was found that lactic acid, glycerine and mannite 



cultures of Aspergillus niger ehcit anaerobic formation of COo. 



On the strength of these results, as well as his numerous later 



experiments with various seed-plants, Kostychev was justified 



in concluding that the so-called anaerobic respiration is peculiar 



to all aerobic plants. Thus Diakonow's thesis was changed. 



Diakonow's results may be traced to a poisoning of the aerobic 



molds in the absence of oxygen by products of imperfect 



metabolism. Kostychev- showed, among other points, that 



Aspergillus niger produces considerable quantities of CO2 and 



' Kostytschew, S. Jahrb. f. wiss. Bot. 40: 563. 1904. 



"- Kostytschew, S. Ber. d. bot. Ges. 25: 44- 1907; Untersuch. iiber anaerobe Atmung. 

 1907. Russian. 



