RESPIRATION AND OXYGEN. 65 



tion, such injury may be greatly reduced. This appUes to fruits 

 in storage as well as to those in transit. 



Noyes (1914 : 792) gradually saturated the soil in which corn and 

 tomato plants were growing with washed CO2. The lower parts of 

 the plants were first affected and in a week the leaves drooped, 

 turned brownish, and withered. The plants were practically browned 

 at the end of 2 weeks' treatment, the tomato showing the most 

 marked effect. After the treatment, oxygen was given access to 

 the plants. The tomato plant soon died, but the corn plant revived 

 and was growing normally at the end of a week. 



Hasselbring (1918 : 284) found that sweet potatoes are killed under 

 an oxygen-pressure of 5 atmospheres, and that starch hydrolysis is 

 greatly depressed or prevented in the killed tissues. The hydrolysis of 

 starch and the formation of cane-sugar take place in the absence of 

 oxygen as in the air or in an atmosphere of oxygen, and the presence 

 of oxygen is thus not always necessary to the formation of cane-sugar. 

 The material consumed and the output of carbon dioxid is greater in 

 the sweet potato during anaerobic than during normal respiration. 



Summary. — The general effect of the reduction or absence of oxy- 

 gen upon respiration is to decrease its intensity, as shown by Godlew- 

 ski, Wilson, Johannsen, Palladin, Stich, Hill, and others. On the 

 contrary, Diakonow found the intensity to be greater in the cotyle- 

 dons of the bean, but this is probably due to their nature as special- 

 ized storage-organs. Even in Penicillium and Aspergillus he found 

 that the production of carbon dioxid ceased immediately upon the 

 withdrawal of oxygen. The reduction in oxygen-content required 

 to affect respiration differs more or less with the species, and this 

 serves in some measure to explain the discordant results. Saussure 

 determined that the oxygen could be reduced one-half without 

 weakening respiration, while Wilson found that the latter was but 

 slightly affected in a mixture containing 20 per cent of air, though 

 distinctly decreased in one with 5 per cent. Stich stated that in 

 general a striking reduction in the amount of carbon dioxid did not 

 occur between 4 and 2 per cent of oxygen. 



Saussure and Grischow concluded that the rate of respiration was 

 somewhat increased in pure oxygen, but Bert observed a decrease in 

 the amount of CO 2 evolved after several days' exposure. While 

 Bohm and Rischawi found that plants were more or less indifferent 

 to high oxygen-content, Godlewski obtained a strikingly greater pro- 

 duction of carbon dioxid for the first day, after which it fell to a mini- 

 mum. Johannsen likewise noted that the respiration intensity under 

 an air-pressure of 10 to 15 atmospheres, corresponding to a pure- 

 oxygen pressure of 2 to 5 atmospheres, was more or less increased for 

 a few hours, after which it gradually decreased to the death point, 

 and the more rapidly under the greater pressure. 



