232 



D. R. Hoagland 



90 

 80 



70 



ft. 



^ 60 



o * 50 



o «• 



u . 



..i 40 



ly W 



W» J 30 



< J 



M — 



te. s 



^ « 20 



lO 



12 18 24 



TEMPERATURE OF SOLUTION -DEGREES C 



SO 



Fig. 3. Effects of temperature on accumulation of potassium in sap by excised 

 barley root systems; each set represents 168 plants, previously grown in a com- 

 plete culture solution for 21 days. 



Absorption period, 10 hours. 



Experimental solution: 



.005 M 

 .005 M 

 .002 M 



KBr 



KNO3 



Ca(N03)2 



The temperatures of the solutions were maintained as shown within approxi- 

 mately plus or minus 0.2° C. 



effects are not restricted to any special type o£ ion. The absorp- 

 tion of both anions and cations is influenced by temperature. 



The importance of soil temperature with special reference to 

 ecology or to practical agriculture is apparent. Seasonal and 

 diurnal changes in soil temperature must influence enormously 

 the rates of absorption of mineral solutes within certain ranges 

 of temperature, and under conditions otherwise favorable to 

 absorption. The general significance of this factor has been 

 emphasized by Lundegardh/ but as yet the relationship of soil 



