62 Fundamentals of Auxin Action 



obtained only after enzymatic activity, gentle hydrolysis or prolonged 

 extraction. Van Overbeek et al (1947) surveyed the distribution of 

 these two types of auxin in the pineapple plant. Using their ether 

 extraction technique, they plotted the flush of auxin obtained in the 

 first hour of extraction as free auxin and that obtained after a passage 

 of time as bound auxin. This distinction appears to be entirely justi- 



Auxin from 

 Leaves 



Auxin from 

 Buds 



12.0 



0.5 



Fig. 29. The auxin content of leaves and buds of a seedling of Vicia fava. The 

 figures represent Avena Einheits of diffusible auxin per hour (Thimann and Skoog, 

 1934). 



fied in view of evidence presented in their paper. In general it ap- 

 peared that free auxin occurred most abundantly at the stem apex. 

 Leaves, whether expanding or mature, yielded only small amounts. 

 In contrast, bound auxin was most abundant in the young expanding 

 leaves, and relatively scarce in the stem apex (figure 30). If the stem 

 apex is unable to produce the large amounts of free auxin which 

 apparently exist there (that is, they do not have the bound form 



