DORMANCY AND 

 DORMANCY BREAKING IN SEEDS 



S. KLEIN 



Department of Botany, Hebrew University, 

 Jerusalem (Israel) 



It would be very helpful if one could start a lecture like this 

 with a clear and physiologically valid definition of what is meant 

 by dormancy. The fact that it was thought desirable to compare 

 this phenomenon in various groups of organism shows that we 

 are still far from a general formula. In the broadest sense, 

 dormancy in seeds means the cessation of growth in the embryo 

 without the latter losing its viability for a prolonged time. The 

 embryo may or may not be enclosed in its natural envelopes. 

 These may consist of an endosperm, a seedcoat and other 

 surrounding layers, which actually do not belong to the 'seed' 

 proper. Since they may all influence the behaviour of the embryo 

 it is more appropriate to talk about dormancy in 'dispersal 

 units' than in seeds^. 



It is evident that such a period of dormancy is of extreme 

 importance in the life of the plant. It allows effective dispersal 

 of the young plants both in space and time, and allows the 

 embryos, which are extremely sensitive in the active state, to 

 overcome conditions unfavourable to development and growth. 



It is also evident that dormancy is closely related to the 

 subsequent renewal of growth. The processes which make this 

 transition possible are therefore of importance in the under- 

 standing of dormancy, and we shall be concerned principally 

 with changes that occur during dormancy breaking and with 

 differences before and after, i.e. between seeds before and during 

 germination. 



This introduces another difficulty, namely, to define what is 

 meant by germination. In order to renew its normal activities, 

 the dormant seed has to be exposed to certain external conditions, 

 e.g., a certain temperature range, water, a certain oxygen level. 



References p. 190 



