188 S. KLEIN 



only respiration at specific times is considered in different 

 batches of seeds. 



This difference in respiration behaviour between 'Hght- 

 treated' and 'dark' seeds may also be found in the presence of 

 inhibitors. It is evident from the Figure that in the light-treated 

 seeds, a 10 mg % dinitrophenol treatment results in a much 

 stronger gas exchange than with 'dark' seeds, although germina- 

 tion is inhibited in both cases. 



In the presence of coumarin, light has a similar tendency to 

 increase respiration, and the tendency increases with the degree 

 of inhibition of germination produced by the inhibitor. In 

 general, light without doubt affects the respiratory apparatus 

 during the germination period. 



It was mentioned earlier that seeds with their coats removed 

 or pricked will germinate even in darkness. What about respira- 

 tion in these? It turns out that their respiration during the first 

 hours is much higher than in whole seeds. Thus, we again arrive 

 at the possibility that gas exchange is limited by the coats and 

 that all that light does is to render the endosperm more pene- 

 trable to gases. Doubts have been expressed whether it is the 

 actual removal or pricking of the endosperm which brings about 

 germination, or whether the stimulation may not be due to the 

 squeezing of the embryo itself during the process of coat 

 removaF. Using deuteron irradiation with a controlled penetra- 

 tion depth into the seed, it was possible to show that it is both 

 necessary and sufficient to affect the endosperm alone in order 

 to bring about germination^^' 21 (Fig. 4). Incidentally these 

 experiments also showed that there is not necessarily a coiTela- 

 tion between germination process and subsequent growth. A 

 small dose of deep-penetrating deuterons bombarding the 

 embryo itself leaves the endosperm unaffected, and therefore 

 does not change the germination pattern, but causes a decrease 

 in subsequent growth. On the other hand, a strong dose of 

 deuterons applied to the endosperm alone will allow complete 

 germination in darkness, without affecting the growth of the 

 seedlings. This deuteron-induced germination cannot be reversed 



