Occurrence and Role of Growth Hormones 65 



appears to be very little free auxin in dormant nieristematic tissues. 

 Until shortly before growtii commences dormant tree buds, seeds, and 

 tubers contain little or no identifiable free auxin. Then, as tree buds 

 begin to grow in the spring, a flush of auxin is produced (e.g. Avery 

 et al, 1937). When seeds are soaked for germination, the auxin pro- 

 duced is so abundant that large amounts actually appear in the soak 

 solution. It will be remembered that in the procedure for the Avena 



.3C 



< 

 < 



z 



LJ 



I- 



O 

 O 



X 



Z) 



< 



20 



40 



60 DAYS 



AGE OF LEAF 



Fig. 32. Changes in ether-exti actable auxin content of bean leaves and petioles with 



age (Shoji et al, 1951). 



test (chapter II) it is imperative to discard the solution in which the 

 Avena seeds were soaked. If the seed is left in the solution rich in 

 auxin from the germinating seed, growth — particularly of the roots — 

 will be inhibited. Again, when potato tubers emerge from dormancy, 

 free auxin becomes detectable in the buds shortly before growth com- 

 mences (Hemberg, 1947). 



The production of auxin by leaves correlates with growth up to 

 the time that maturity is reached. For example, in figure 32 the diffusi- 



