ECOLOGICAL PROBLEMS OF SEED DORMANCY 



D. ROLLER 



Department of Botany, 

 Hebrew University, Jerusalem (Israel) 



Dormancy in seeds is a misleading term. A seed which does 

 not germinate when placed in moist soil is just as dormant as a 

 plant which does not flower during long days because it requires 

 short days for flowering. The only dilTerence between the two is 

 that in the case of the seed we are dealing with initiation of 

 growth while in the other we are dealing with initiation of 

 flowering. In both cases the process of initiation is triggered and 

 controlled by environmental signals, and may be said to be 

 regulated by the environment^. Some seeds require a period of 

 so-called 'after ripening' under a specific range of environmental 

 conditions before they are ready to germinate-^"^, and analo- 

 gously many plants require a certain period of vegetative 

 growth under a specific range of environmental conditions 

 before they achieve 'readiness to flower'. Also, many seeds are 

 known to become less dormant as they age, insofar as they 

 germinate within a wider range of environmental conditions^' ^. 

 and analogously many plants which require a certain photo- 

 period or vernalization for flowering may eventually flower 

 without them when they are sufficiently old. 



If we accept this analogy we may approach the question of the 

 significance of these phenomena in the existence of the species. 

 The common denominator for these phenomena is the existence 

 of a biological system which permits a choice between starting 

 a new developmental phase and continuing in the previous one. 

 It is logical to assume that such systems have evolved as a result 

 of their being of survival value to the species. Presumably a 

 photoperiod-sensitive plant utilizes the most dependable time- 

 telling device, the astronomical clock, to choose the time of 

 flowering suitable for that particular species in its particular 

 habitat to carry out to completion one essential part of its 



References p. 162 



