50 



effect of aeration on the protozoa, nematodes, fungi, 

 algae and other non-baterial organisms of the soil, 

 but it is probable that most of them are aerobic and 

 perish or pass into resting stages when aeration is de- 

 ficient ♦ Whether these changes are, as a rule, bene- 

 ficial or injurious to higher plants it is impossible 



to say. 



c 

 In connection with the uncertainties as to the 



cause and even the reality of the effect of soil aeration 

 on plants it is interesting to note that a similar con- 

 flict of evidence occurs in the matter of the aeration 

 of the nutrient solution when plants are grown in water- 

 cultures. Aeration of the solution (by shaking or by 

 blowing air through it J has been found beneficial by 

 Wilms, Aiker,^ Ehrenberg,^ and Underwood 5 and some 



1. On protozoa see Koch,- Jour. Agr. Res. 4: 

 511-559(1915). On nematodes see Cobb,- U. S. Dept. of 

 Agr., Yearbook 1914 ; 457-490 (1915). On fungi see Waks- 

 man,- Soil Science 2: 103-155 (1916). 



2. Jour. landw. 47: E61 (1899). 



3. Inaug. Diss., Erlangen, p. 72 (1900). 



4. Zeits. fur rflanzen krankh. 16: 193 (1905). 



5. Hall, Brenchley. and Underwood,- Phil. Trans 

 Roy. 3oc. (London), B, 204: 179-200 (1913). 



