91 



showed decreases with both carbon dioxide and hydrogen 

 much like those observed with living plants of Phaseolus 

 but Slightly less in amount. 



Prom the present viewpoint the significant 

 things in these experiments are, first, the injury by 

 hydrogen and, second, the fact that injury consisted 

 in an interference with water absorption. The importance 

 of this second conclusion will be apparent when the 

 experimental results of the present investigation are 

 presented. The action of hydrogen implies a need of 

 the roots of Phaseolus for oxygen but the evidence leaves 

 much to be desired in precision and finality especially 

 since it was obatined in water-culture and since the 

 other evidence concerning the effect of aeration in 

 water cultures is so seriously contradictory. The 

 evidence of the detrimental effect of carbon dioxide 

 both in soil and in water-culture appears to be con- 

 clusive but means nothing for the problem of the oxy- 

 gen requirement of the roots. 



The experiments of Gannon 2 have been made 

 incidentally to an investigation of the distribution 



i. See pages 2>0'—S~/ 



2. Gar. Inst, of V/ash. , Yearbook 11: 62 (1912), 

 14: 62-64 (1916), 15; 74-75 (1916); Amer. 2our. Bot. 

 2: 211-224 (1915); Amer. Hat. 50: 455-442 (1916); 

 Science, 44: 761 (1916). See also Gannon and Free,* 

 Science 45: 178-180 (iyi7). 



