PLANT HORMONES AND SEED DORMANCY 167 



TABLE I 



THE EFFECT OF LIGHT AND GIBBERELLIN TREATMENTS ON THE GERMINATION OF 



LETTUCE SEEDS 



Results given as percent germination. The red illumination was given after 

 two hours' imbibition. The Far Red was given either immediately after the 

 Red or, when given alone, after 30 min of imbibition. The concentration 

 of the gibberellic acid was 2.9 x lO^' M '. 



germination, while in the absence of kinetin 3600 ft.c.s. are 

 necessary to bring about the same result^^. 



In all these cases it is not clear what are the actual mechanisms 

 that are affected either by light treatment or by the hormones. 



The possibility that lAA may play a part in the germination of 

 seeds has been considered for many years, but the results of the 

 experimental work were rather contradictory. Some suggested 

 an inhibition of germination by excess of auxins present in the 

 seedsorinthefruits^^' i^, while others suggested stimulation^^' ^^. 

 Soding and Wagner^^ tried to settle this controversy by suggest- 

 ing that lAA stimulates the germination of dormant seeds but 

 does not affect the germination of non-dormant ones. They 

 tried unsuccessfully to test this hypothesis on Poa seeds but 

 the idea proved to be correct for lettuce seeds^^"-^' ^^. The 

 more dormant the seeds were, and the lower the temperature 

 during germination, the more effective was lAA in breaking the 

 dormancy and in stimulating germination. 



The next step was, therefore, to find out whether the seeds 

 contain any endogenous lAA and whether its amount changes 

 during germination. Dry seeds and seedlings of lettuce of varying 



References p. 172 



