27 



to the square of the absolute temperature and Inversely- 

 proportional to the total pressure of both gases, 1 

 The constant for the diffusion of oxygen into nitrogen 

 has been determined by Obermeyer 2 for 0° G. and for 

 760 mm, pressure, as ,171, The average temperature of 

 plant roots is probably about 20° C (293° absolute). 

 The constant for this temperature and for atmospheric 

 pressure (760 mm.) would be to ,171 as 293° is to 273°, 

 or ,197. For the assumed case, "s" (the area of the 

 tube) equals ~P~ times the square of the radius, or 

 •007854 square centimeter. We take the time as one hour 

 or 3600 seconds. The change of partial pressure (or 

 concentration) of oxygen is from ,2 atmosphere at the 



1. These relations are approximate only but 

 will suffice here. For details see Stefan,- Sitzungs- 

 ber. Akad. Wiss., Wien, math.-naturw. kl. 63: 63 (1878); 

 Loschmidt,- Sitzungsber. Akad, Wiss., Wien, math.- 

 naturw. kl, 61: 36 7 (1870), 62: 468 (1871); Oberneyer,- 

 Sitzungsber, Akad. Wiss., Wien, math.-naturw. kl., 85: 

 147, 748 (1880}, 87: 188 (1881), 96: 546 (1883). 



2, loo, cit .. Through Smithsonian Physical 

 Tables, 6th ed., reprint, p, 140 (1916), 



