/3* 



pressure of the oxygen. 1 Thus oxygen will oe obtained 

 quite as well from an atmosphere of low oxygen content 

 as from one of high if both atmospheres are sufficient 

 in total volume or are renewed sufficiently often* 

 If this is true and if the observed root injury is due 

 to interference with respiration, the roots should be 

 able to endure a low percentage of oxygen in the soil 

 atmosphere if the atmosphere is renewed sufficiently 

 often. The agreement of the Goleus results with this 

 prediction is not as complete as might be desired. At- 

 mospheres containing 2, 6 and 10 percent of oxygen 

 were found to be injurious, though they were changed 

 daily. Even the simple enclosing of the soil, the out- 

 let tubes remaining open, was injurious in some cases. 

 Sealed plants grew in completely normal manner only 

 when supplied with pure oxygen or when air was actually 



1. See authors cited in note , page 

 also: Godlewski,- Jahrb. wiss. Bot. 13: 491-522 (1882); 

 Stich,- Flora 74: 1- (1896); Pfeffer,- Physiology of 



Plants, vol. 1, p. 53y (1900); Czapek,- Biochem. der 



U. 



Pflanzen, vol. 2, p. 394 (1905); Eyler,- Pflanzenchem. 



vol. 2 & 3, p. 166 (1909); Bayliss,- Prin. General 

 Physiol, pp. 608-609 (1915). 



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