Factors Altering Effectiveness 145 



to a small local area on one leaf. The distribution was determined by 

 autoradiography as illustrated in figure 67. One hour after applica- 

 tion the plant was cut into several pieces, and the autoradiograph 

 showed that already the auxin had permeated to the stem and to the 

 opposite leaf in part. The rate of movement was estimated at aboiu 

 4 cm. per hour. 



Fig. 67. The movement of radioactive 2,4-D in bean plants when applied in 

 kerosene oil. (A) Rings attached to leaves to assure localization of application on 

 leaf surface. (B) Autoradiograph of a plant dismembered 1 hr. after 2,4-D applica- 

 tion. (C) Autoradiograph of a plant not dismembered after 2,4-D application (Rice 

 and Rohrbaugh, 1953). 



