Occurrence and Role of Growth Hormones 



63 



from which to produce free auxin), then it would seem Hkely that the 

 adjoining young leaves, rich in bound auxin, may be the primary 

 source of the free auxin which appears at the stem apex. 



Free Auxin 



Bound Auxin 



Fig. 30. Diagram of the distribution of free and bound auxin in the vegetative 

 pineapple plant. Figures represent microgram equivalents of indoleacetic acid per 

 kg. fresh weight (van Overbeek et al, 1947). 



Surveys of auxin distributions in other plants have been made and 

 the highest auxin concentrations found in some of these are listed in 

 table 5. It seems evident that the greatest quantities of auxin charac- 



TABLE 5 

 Some Examples of Auxin Concentrations Found in Plants 



