possess special aerating systems and it is by no means cer- 

 tain that these systems, even when present, are adequate 

 for the transfer* of respiratory oxygen to the remoter 

 organs such as the roots. The cultural benefits of soil 

 aeration may be ascribed, with much probability, to sec- 

 ondary chemical and bacteriological changes in the soil 

 rather than to direct effects m root respiration. Hot 

 is there lacking direct evidence against the assumption 

 of the necessity for free oxygen in the soil. Foe instance, 

 roots of some plants are known to penetrate many feet 

 into the soil. Other roots live habitually, or may live 

 for a time, in the water- saturated soils of marshes and 

 stream banks. It is difficult to see how such deep- 

 lying or hydrophyllous roots can obtain any considerable 



pply of atmospheric o::ygen even when all possible al- 

 lowance is made for supply by means of internal aerating 



systems. 



Because of these uncertainties and conflicting 



implications it seemed desirable that the whole matter 

 be reviewed, both with regard to information available in 

 the literature and from practice, and by actual experi- 

 ment. 2he results of this review are embodied in the 

 present paper. I am indebted to Pr feasor B. E. 

 Livingston for the suggestion of the problem and for 

 much detailed and invaluable advice, assistance and in- 

 spiration in the planning of the experimental work. 

 am also indebted to Dr. ... - Oannon'of the Department 



