142 Fundamentals of Auxin Action 



through the plant. If the auxin is held in the leaves only and is not 

 translocated to the lower parts of the plant a systemic effect will not be 

 obtained. This is especially undesirable in herbicide work. If the 

 auxins are not translocated through the plant the foliage may be 

 killed and the stem and other essential parts left unharmed. 



Environmental Factors 



The effects of some environmental conditions upon translocation 

 of 2,4-D in bean leaves have been studied by Rice (1948) who con- 

 cluded that the translocation was unaffected by temperature differ- 

 ences ranging from 50° to 90° F. On the other hand, he confirmed that 



--f 



72 HRS. 



TIME 



Fig. 66. Translocation of 2,4-D as evidenced by inhibition of leaf weight of young 

 expanding leaves after application, comparing translocation in dark, in weak light 

 (100 f.c), and in strong light (900 f.c.) (Rice, 1948). 



light exerts a profound effect upon translocation and that this effect is 

 proportional to the intensity (figure 66). Rice applied 2,4-D on the 

 primary leaf of bean seedlings and used as a criterion of translocation 

 the effect of the auxin in inhibiting enlargement of the trifoliate leaf 



