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PREVIOUS EXPERIMENTS Oil THE OXYGEN REQUIREI.IEIIT 



OP PLMIT RuOTS. 



There have been mentioned above two series 

 of investigations which throw, indirectly, some light on 

 the need of roots for oxygen though neither line of ex- 

 perimentation is conclusive or satisfactory. Eirst are 

 the observations on the rate of respiration of various 

 roots. -^ It has already been indicated that these are of 

 little significance for the reason that the observed 

 occurrence of normal aerobic respiration in the presence 

 of oxygen does not prove that the same tissue could not 

 respire anaerobicaily if oxygen were withheld. Second 

 are the experiments of Jentys, Chapin, IJoyes, and others 

 in which the normal soil atmosphere was replaced by 

 carbon dioxide, resulting in more or less serious injur- 

 ies to the plants. One result of such replacement 

 is to deprive the roots of oxygen but it is by no means 

 certain that this deprivation is the sole cause of the 

 observed injury or that it is a cause of injury at all. 

 Hot only do the probable specific effects of carbon 

 dioxide come into play but the possible presence of 

 traces of oxygen, possible variations of water supply, 

 individual plant variation, and the like were not taken 



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