138 



Fundamentals of Auxin Action 



(1948) has shown that the absorption of 2,4-D is considerably more 

 rapid at 90° than at 50° F. In figure 63 it can be seen that, while 

 absorption of simple aqueous solutions was somewhat greater at the 

 higher temperatures, the absorption of a solution including a fatty 

 carrier (Carbowax 1500) showed a much greater temperature differ- 

 ential. With Carbowax in the spray, the final absorption at 90° F was 

 nearly three times that occurring at 50° F. These studies were carried 

 out by applying known quantities of 2,4-D solution on the leaf, wash- 

 ing off the unabsorbed auxin, and measuring it quantitatively by 

 spectrophotometric determination. 



20 



:3 



No Carrier 



L — 



oft. ■ .. 



72 HRS 



TIME AFTER APPLICATION 



Fig. 63. The time course of absorption of auxin (2,4-D) by bean leaves at three 

 different temperatures with and without a carrier, Carbowax #1500 (Rice, 1948). 



Although the total absorption is greater at higher temperatures, 

 the duration of absorption is apparently reduced by warmth in the 

 absence of a carrier; in other words, the rate of absorption is in- 

 creased by higher temperatures, but the time over which the absorp- 

 tion occurs is somewhat decreased. This may be presumed to be an 

 effect of the more rapid drying of the spray droplets at the higher 

 temperatures. 



