222 moderator: s. hestrin 



can induce dormancy by 16 long days, and break it by 3 short 

 days. All the stages of the life cycle manifest this response 

 pattern. I tried it out both on the whole gametophyte and on 

 the thallus which I had cut into pieces, and obtained the same 

 results in both. Another advantage of this material is that the 

 gemmae — the vegetative reproductive organs are genetically 

 uniform. Dormancy can be induced in them in the gemmacurp. 

 One can thus obtain at will either dormant or nondormant 

 gemmae. We have so far observed these phenomena but know 

 very little about the biochemical behaviour. The suitable 

 temperature for growing this material is about 15° and the 

 required light intensity about 120 ft.-c. 



Moderator: This seems to be truly a most attractive and 

 uniquely suitable biological material for the study of dormancy. 



(VI) Memory Phenomena in Dormancy 



Moderator: Several of the speakers have pointed to the 

 operation of the memory phenomena in relation to induction 

 and duration of dormancy in different systems. What might be 

 the physical basis of these effects? 



Lees: The mechanism controlling diapause termination 

 provides a kind of memory, usually of past temperatures which 

 are integrated in a very particular way. As a model system we 

 could suppose that two chemical reactions are competing for a 

 given substrate; or, simply, that there are opposing synthetic 

 and breakdown reactions. In both cases the reaction must have 

 different temperature coefficients. As yet we have no inkling as 

 to what these hypothetical reactions might be. 



The neurosecretory cells are involved in another type of 

 memory when, in diapause induction, they 'record' the photo- 

 periodic stimulus even though its effect is not manifested until 

 much later in development. The photoperiodic measurement of 

 time itself involves a third kind of memory, the nature of which 

 is still largely obscure. 



