73 



of aerobic roots. Oxygen absorbed by rain water is 

 carried downward as the water enters the soil and proba- 

 bly forms an important contribution to the soil supply. 

 Harrison and Aiyer 1 regard this form of aeration as 

 very important in the growing of rice on wet soils 

 and suggest that the oxygen content of the downward- 

 percolating water is greatly and beneficially increased 

 by means of oxygen produced by green algae growing on the 

 soil surface. The solubility of oxygen in water is some- 

 what greater than the solubility of nitrogen. Accordingly 

 the gases absorbed by natural waters contain relative- 

 ly more oxygen and less nitrogen than does the air. 'Jater 

 in contact with air at 20° G. and normal atmospheric 

 pressure (760 mm.) absorbs 6.36 c.c. of oxygen and 

 12.32 c.c. of nitrogen per liter of water. This gives 

 a total absorption of 18.68 c.c. of both gases, in 

 which mixture the oxygen forms 34.03 percent (by volume] . 



1. i.iemoirs Dept. Agr. India, Dhem. Ser, 3_: 

 65-106 (1913), 4: 1-17 (1914). 



2. "./inkier,- Ber. Chem. Ges. 24: 3609 (1891). 

 On the diffusion of oxygen in water see Carlson,- Jour. 

 Amor. Ghem. 3oc. 33: 1027-1032 (1911). ^he carrying 



of oxygen into the soil by water is probably not dif- 

 fusional but due entirely to mass movement of the water. 



