52 



The inferential evidence concerning the need 

 of soil aeration and of aerobic root respiration which has 

 been discussed in this chapter may now be summarized. 

 It should be noted that there are two subjects of inquiry - 

 soil aeration and root respiration - and that they are 

 not necessarily the same. Even were anaerobic root respira- 

 tion always possible, adequate soil aeration might be nec- 

 essary in order to prevent injurious reaction on the soil 

 micro-organisms or the formation of injurious chemical 

 compounds. On the other hand, aerobic root respiration 

 might be a universal necessity and soil aeration neverthe- 

 less unimportant, because of the natural aeration of soils 

 being always sufficient for the needs of the roots. 



The evidence concerning root respiration is: 

 (1) analogy with other plant organs, (2) the experimental 

 discovery of normal, aerobic respiration in the case of 

 certain roots, and (3) the possession 4$ certain roots 

 of special morphological arrangements apparently adapted 

 to facilitate aeration. The argument by analogy is worth- 

 less since many organisms can respire anaerobically for 

 indefinite periods and most organisms appear to be able to 

 do so for a limited time. Similarly the observation of 

 aerobic respiration in roots does not prove anaerobic 

 respiration impossible, even for those particular roots, 



1. This has been urge* by Mitscherlich,- 

 Bodenkunde, 2nd ed., p. 151 (lyiZ). 



