SEED DORMANCY AND DORMANCY BREAKING 



187 



4 8 12 15 20 24 



Hours 



8 12 16 20 24 



Fig. 3. QO2 and QCO2 of lettuce seeds (Grand Rapids). The straiglit line 

 at 100 is the QO2 and QCO2 respectively in darkness and water, to which 

 all the other values are related. QO2 and QCO2 respectively of seeds imbibed 

 in water, which were illuminated for 30 seconds with 250 ft.c. of red light 

 after 2 h of imbition (O — O). QO2 and QCO2 respectively of seeds imbibed 

 in 10mg% dinitrophenol and illuminated (_!_ — _). QO2 and QCO2 

 respectively of seeds imbibed in 10 mg°o dinitrophenol in the dark (▲ — A). 



dark. In illuminated seeds, imbibed in water, there is a small 

 rise in rate during the first 12 h; this was found to be highly 

 significant. The total amount of gases taken up or evolved during 

 this 12-h period is higher, but not significantly so, in illuminated 

 than in 'dark' seeds. This is because in discrete batches of 

 illuminated seeds, the rate of gas exchange sometimes starts at 

 a lower level and sometimes at a higher one than in 'dark' seeds. 

 The main consideration is that respiration is affected in illumi- 

 nated seeds. The difference in respiration between illuminated 

 and non-illuminated seeds is seen in the tendency to rise of the 

 exchange rate and not necessarily in the overall amount of gas 

 exchange. It can, therefore, easily be overlooked, especially if 



References p. 190 



