164 D. KOLLER 



Keynan: Is this light sensitivity not a means for the seed to 

 know that it is at the right depth for germination? 



Koller: This is unlikely, as lettuce seeds planted in the soil 

 are no longer light sensitive. 



Nachmony: The temperature range may be another expla- 

 nation. Wareing found that the germination of Betula seeds at 

 15° can be induced by photoperiodic treatment, while at 26° a 

 flash of light was sufficient to initiate germination. 



Koller: In our laboratory germination was independent of 

 light at 20° or below. 



Lees : Germination in the dark might be equivalent to germi- 

 nation in continuous light. 



Galun : What is the ecological value of low oxygen tension? 



Koller: Marsh plants germinate only under marsh con- 

 ditions. I would like to remark that we cannot generalize about 

 'normal' conditions, since every variety has its conditions for 

 germination, and the dormancy of the seed may be dependent 

 on the availability of these specific conditions. 



