SEED GERMINATION 543 



It is most important that the light effects on the germination of lettuce 

 seeds and photoperiodic responses seem to be identical. 



Evenari and Stein (1953) proposed a somewhat different theory of 

 photoblastism. The fundamental process involved in the induction of 

 germination consists in an electron transfer from a dye A with an absorp- 

 tion peak at about 6600 A: 



A + hvi -^ .4 *. 



An excited molecule A * is formed which may lose its excited electron to a 

 neighboring trap: 



A*^A+-{-etr. 



The absorption peak of the new system shifts to approximately 7300 A. 

 The absorption of a quantum of suitable energy will bring about the 

 release of the trapped electron, 



■ A+ + Ctr + hv2^ A. 



An increase in temperature may also supply the energy of activation for 

 liberating the electron from the potential well. The entire metastable 

 system may be one belonging to the original absorbing molecule. Oxygen 

 would react with the original dye with total or partial electron transfer, 



A -{- Oo^ A+ ■ ■ ■ -O 



2- 



According to this scheme, the odd ion A+ is of paramount importance 

 for germination, since it would initiate germination either in that form 

 or through its associated free radical B, where 



5 + H+ ^ A+. 



REFERENCES 



Adams, J. (1927) The germination of the seeds of some plants with fleshy fruits. 



Am. J. Botany, 14: 415-428. 

 Andersen, A. M. (1932) The effect of removing the gkimes on the germination of 



seeds of Poa compressa. Am. J. Botany, 19: 835-836. 

 (1947) The effect of alternating temperatures, light intensities and moisten- 

 ing agents of the substratum on the germination of freshly harvested seed of 



Oregon grown ryegrass. Proc. Assoc. Offic. Seed Analysts N. Amer., 37: 152- 



161. 

 Arnaudov, N. (1929) Beitrag zur Keimungsphysiologie der Tabaksamen. Ann. 



Univ. Sofia Fac. Phys.-Math., Ser. II, 25: 143-157. 

 Axentieff, B. N. (1929) Ueber die RoUe der Schalen von Samen und Friichten, die 



bei der Keimung auf Licht reagieren. Botan. Centr. Beih., Abt. I, 46: 119-202. 

 Baar, H. (1912) Ueber den Einfluss des Lichtes auf die Samenkeimung und seine 



AbhJingigkeit von ausseren Faktoren. Sitzber. Akad. Wiss. Wien, Math, naturw. 



Kl. Abt. I, 121: 667-705. 

 Becker, H. (1913) Ueber die Keimung verschiedenartiger Frtichte und Samen bei 



derselben Spezies. Botan. Centr. Beih., Abt. I, 29: 21-143. 



