45 



are usually unlike and probably would not respond in an 

 entirely identical manner to the removal of oxygen. In 

 the experiments with Goleus three quite different loams 

 from different localities were used and were mixed with 

 varying proportions of sand. Some of the soils were 

 high in organic matter, some were low. Some were light 

 in texture, some were fairly heavy. With all of these 

 varied soils the results were completely identical, 

 both in the conditions determining the occurrence of in- 

 jury and in the symptoms of the injury which occurred. 

 This absence of any dependence of the results on the 

 nature of the soil implies that such modifications of 

 the soil micro-flora as occur under the conditions of 

 these experiments are without important influence on 

 the roots. It is highly probable that the injuries 

 observed are due to changes in the roots themselves 

 which changes result directly from the shortage of 

 oxygen. 



The pbvious hypothesis as to the mechanism 

 of these injuries is that they are due to direct in- 

 terferences with the respiration of the root protoplasm. 

 It is probable that any tissue which requires free oxygen 

 for respiration can absorb this oxygen from any atmo- 

 sphere in which oxygen is present in sufficient total 

 quantity, regardless of the percentage or partial 



