60 AERATION AND AIR-CONTENT. 



to 5 atmospheres at first increased the evolution of C0 2 for the differ- 

 ent seedlings investigated and in varying degree for the different 

 species. With longer action, the C0 2 decreased gradually until 

 death ensued, and the more rapidly, the greater the pressure. After 

 two to four hours' exposure to oxygen of a pressure of 2 to 5 atmos- 

 pheres, the plants showed a considerably greater evolution of COz 

 than before the exposure when they were again returned to the 

 original conditions. 



Pfeffer (1885 : 645) found that the amount of C0 2 evolved when 

 seedlings were placed in hydrogen was regularly less than in the air. 

 Respiration in the latter was often several times greater, with the 

 exception of Viciafaba, where the amounts were about equal. The 

 respiration of sun-roses in ordinary air, in mixtures of equal parts of 

 air and hydrogen, and of 1 part of ah- and 4 parts of hydrogen was 

 essentially the same. Intramolecular respiration, as shown by a 

 considerable decrease of the C0 2 produced, occurred in a mixture 

 of 19 parts of hydrogen and 1 of air. 



Diakonow (1886 : 411) demonstrated that the excretion of carbon 

 dioxid by cotyledons of the bean was 50 per cent greater in the ab- 

 sence of oxygen than in its presence. He reached the conclusion 

 that fermentation begins immediately upon the withdrawal of oxy- 

 gen and disappears again just as soon as the cells resume their full 

 capacity for respiration. As a consequence, there can be no respira- 

 tion, and hence no life, without the presence of oxygen or the action 

 of fermentation as the one means of meeting the energy needs of 

 the cell. 



Palladin (1886 : 44) determined that rootlets of Vicia faba con- 

 sumed 4.6 per cent of dry material in 20 hours of normal respiration, 

 and 11 per cent during the same period in air free from oxygen. 

 Since they used more than twice as much dry substance in the latter 

 in spite of the gradual decrease of activity, anaerobic respiration 

 must be regarded as true fermentation. 



Clausen (1890 : 893) investigated the behavior of dead protoplasm 

 with respect to the evolution of C0 2 and also the decomposition of 

 albumen in the living protoplasm when oxygen is absent. With 

 reference to the former, he found that living plants evolved 27 to 28 

 mg. of C0 2 in an hour, while the same plants when killed gave from 

 1.5 to 2.1 mg., which was little more than within the limits of error. 

 He concluded in agreement with Detmer, Johannsen, and Pfeffer, 

 and contrary to Reinke's opinion, that dead plants do not evolve 

 CO 2 . The albumen of the protoplasm of plant-cells when this is 

 in contact with oxygen, as is well known, breaks down into acid 

 amides and amino-acids, and his experiments showed that a similar 

 breaking-down occurred in the absence of oxygen. 



Stich (1891 : 1) concluded that respiration is independent of the 

 oxygen-content of the environment within fairly wide limits. With 



