266 Auxins in Agriculture 



of such inhibitors has been ably reviewed by Evanari (1949). The 

 specific demonstration that growth inhibitors are directly involved in 

 dormancy has been made only recently by Hemberg (1949). He has 

 found that dormant potatoes and dormant tree buds contain sub- 

 stances which are strong inhibitors of growth, as analyzed in the 

 Avena test. Furthermore these inhibitors disappear from the plant as 

 dormancy is broken either naturally or artificially. The presence of in- 

 hibitors of growth in dormant ash buds collected in October can be 

 seen in figure 110. In February as the bud emerges from the dormant 

 condition, the inhibitors disappear. The same situation has been found 

 to exist in potato tubers (Hemberg, 1952). Furthermore, chemical 

 treatments which break dormancy likewise cause the disappearance of 

 these growth inhibitors. A striking example of this induced disap- 

 pearance following ethylene treatment to break dormancy is shown 

 in figure 111. Extracts of peelings from dormant potatoes produced 

 a fairly constant inhibition of Avena curvature during the test period, 

 but extracts from ethylene treated potatoes showed a nearly complete 

 disappearance of the inhibition effect in a period of six days after 

 treatment. 



Guthrie (1940) has found that the ethylene treatment of potato 

 tubers breaks dormancy and causes the appearance of relatively large 

 amounts of glutathione. Glutathione has been shown by Hemberg 

 (1950) to cause the disappearance of the growth inhibitors associated 



30 



40 



50 MG 



AMOUNT OF BUD EXTRACT ADDED 



Fig. 110. The inhibitory and non-inhibitory effects of extracts of dormant 

 (October) and non-dormant (February) ash buds as measured by the Avena test. 

 The samples were added to a constant amount of indoleacetic acid (data of Hem- 

 berg, 1949). 



