376 PLANT GROWTH SUBSTANCES 



concentrations higher than those in any other plant tissues. Crude 

 preparations of natural growth hormones specific for fruit setting have 

 been prepared from the pollen and young fruit of several economic 

 plants (15,26,45,53). Continuing efforts in the isolation of these natural 

 growth substances should provide the key for the further elucidation of 

 the many still baffling problems associated with the control of fruit 



settmg. 



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