I IUCTIC . , 



The general opinion that a high degree of soil 

 aeration is necessary to the proper respiration of plant 

 roots and hence to favorable growth proves, on exi mina- 

 tion, to have a very inadequate basis of observed fact. 

 Actual experimentslon the respiration of roots i 

 meagre and inconclusive. Experiments and observations 

 on the practical benefits of improved soil aeration are 

 more numerous but nearly all of them have lacked ade- 

 quate controls or have failed to take into account the 

 ny chemical, bacterial and other secondary reactions 

 which are known to complicate the problem. The assump- 

 tion of the dependence of root respiration upon ade- 

 quate soil aeration appears to have arisen largely 

 from various items of indirect and inferential evidence 

 which may be summarized under t" :eads: The kr 

 neeessity of oxygen for the respiration and life of 

 protoplasm in general; '2ho possession by plants of I: - 

 ternal aerating systems and other morphological devices 

 pear to be useful in supplying oxygen to organs 

 not directly exposed to the air; Che observed benefi- 

 cial effects of good aeration in cultural practice. 

 The implication of these evidences trong but cer- 

 tain contrary indications are also known. - stance, 

 some organisms and parts o: nisms do not require 

 free oxygen for respiration. Again manj nts do not 



