40 



Fundamentals of Auxin Action 



the primary effects of a carrier is to increase the time over which 

 absorption takes place. Whether the rate of absorption is altered is 

 not clear. The data in the figure suggest that the rate of absorption 

 might be somewhat reduced by the carrier, even though the total 

 absorption is increased. The use of more viscous carriers such as 

 lanolin paste permits an even greater dination of absorption. 



The rapidity of absorption of auxin sprays can be seen in the 

 inability of rain to vitiate the effect, even when the rain occurs very 

 soon after the spray has been applied. Studies of the effects of rain at 

 various intervals after auxin sprays to prevent preharvest drop of 

 apples (Overholser el al, 1943) show that simulated rain applied four 

 hours after auxin application did not perceptibly reduce the auxin 

 effect. A more elaborate study of this sort by Weaver et al (1946) 

 established that when auxin is applied as the acid form in water, entry 

 is nearly complete in one hour, and full effectiveness is attained in six 

 hours. Data from two such experiments with simulated rain are given 

 in figure 65. In the same experiments, the auxin was applied in diesel 

 oil to other plants, and rain only fifteen minutes after the spray did 

 not reduce the effectiveness at all (figure 65). 



E 

 o 



LlI 



< 



LJ 



-Control 



— -^Control 



3 . 



2 • 



) -^Control 



2,4-D IN WATER 



2,4-D IN OIL 



15 



20 HRS. 



TIME ELAPSED BEFORE RAIN 



Fig. 65. The effects of rain applied artificially at various intervals of time after 

 2,4-D spray. Two sample experiments for 2,4-D in water and in oil, at an estimated 

 0.65 lbs/acre, followed by rain of one inch. Inhibition of leaf weight taken as index 

 of the amount of absorption (from Weaver et al, 1946). 



