THE EFFECT OF EXTERNAL CONDITIONS UPON THE 



AFTER-RIPENING OF THE SEEDS OF 



CRATAEGUS MOLLIS 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 1 57 



Wilmer E. Davis and R. Catlin Rose 



It is well known that the seeds of many plants do not germinate 

 immediately after ripening, but only after a period of rest which in 

 some cases no doubt extends into years. Nobbe and Hanlein (16), 

 for example, kept certain weed seeds under germinating conditions 

 for a period of 1173 days without germination. 



While various workers have done much in the way of adding to 

 the list of seeds that require a rest period before germination, little 

 has been done to determine the real cause of this delay or dormancy 



During this period, it is assumed that the 

 tianges, at the completion of which germina- 



on the part of the seed. 



may take place. This period of preparation for germination 



een termed the 

 may be made 



The term after-ripening 



limit 



germination; changes involving the release 

 piratory enzymes, thus leading to rapid metab 

 m or other modifications of incasing structure 

 r or oxygen supply or even mechanically 1 



growth. But in relatively few cases do we know to which of these 

 dormancy is due. In most literature the cause is assumed to be 

 the need of protoplasmic changes in the embryo. In this paper 

 we have used the term after-ripening in reference to embryonic 

 changes whether protoplasmic or metabolic, in contrast to those 

 changes that merely affect the incasing structures. By germination 

 we mean the growth of the hypocotyl. 



Many more or less successful attempts have been made to 

 shorten or eliminate altogether this period of inactivity on the part 

 °f the embryo by certain stimuli designed to arouse the dormant 

 protoplasm to activity. Lately Fischer (5) observed that seeds of 

 certain water plants might be kept in water free from fermentation 



4 9 [Botanical Gazette, vol. 54 



