T. C. Broyer 207 



A study was made (/j) of the possible effects of temperature and 

 aeration on exchange adsorption with roots. The results of these studies 

 are summarized in Figures 11, 12A, and 12B. In Figure 11, the rates of 

 outward isotopic diffusion and exchange of potassium at two tempera- 

 tures are shown. Simple diffusion of salt from roots into distilled water 

 was very slow; exchange of cations was rapid. About 10 per cent of the 

 previously absorbed radioactive isotope of potassium was readily ex- 

 changeable (compare with data of Overstreet and Jacobson, referred 

 to later for other cations and for anions). The rates of ionic exchange 

 were not significantly influenced by temperature. In Figure 12, a similar 

 experiment on exchange at two aeration levels is presented. The upper 

 graph (12A) shows the relative accumulation of radioactive potassium 



2 3 



TIME IN HOURS 



Figure 12B. Effects of aerobic and anaerobic culture medium environments 

 on the rate of outward movement of radioactive potassium. Following the du- 

 plicate treatments presented under Figure 12 A, individual sets of excised roots 

 were exposed to culture solutions of o.oo^N KC1 at 20. 5 C. as follows: 



Pretreatment — Absorption of K*C1: A-B, temperature 0.5 ° C, air-treated 

 culture; C-D, temperature 20.5 ° C, air-treated culture; E-F , temperature 20.5 ° 

 C, N 2 -gas-treated culture. 



Treatment during efflux study: A, CO a -free air passed through culture solu- 

 tion; B, CO,-free N 2 gas passed through culture solution; C, C0 2 -free air passed 

 through culture solution; D, CO a -free N 2 gas passed through culture solution; 

 E, C0 2 -free air passed through culture solution; F, C0 2 -free N 2 gas passed 

 through culture solution. 



