6o BOTANICAL GAZETTE [July 



ripening goes on equally well in dark or light. At a temperatu 



imum, but not sufficiently 



some 



is indicated in table III. 



The seeds of the hawthorn will germinate at a temperature 

 slightly above o° C. We have found them in nature germinating 

 in early spring, when the ground was yet quite cold and wet. 

 Seeds placed on ice for after-ripening germinate in this condition 

 after going through that process. The germination, however, takes 

 place irregularly, and often requires a considerable period before all 

 the seeds of the culture are germinated. But if the seeds are 

 removed from the cold when they show signs of germinating, and 

 placed at the temperature of the greenhouse, the germination takes 

 place very rapidly, often reaching 90 per cent or more within two 

 or three days. The sudden change of temperature when the after- 

 ripening is complete acts as a powerful stimulus to germination, 

 but if after-ripening is not complete, it seems to inhibit the latter. 



How widespread this condition of seeds is, which requires after- 

 ripening, that is, some change involving the embryo itself before 

 germination becomes possible, is not known. All seeds that are 

 slow to germinate, from whatever cause, have too frequently been 

 put into this class. In most cases the delay is evidently not to be 

 found in the embryo at all, but in the seed coat or some other 

 external structure which prevents or limits the taking up of water 

 or oxygen or mechanically inhibits growth. The only way to 

 determine whether the delay is due to after-ripening or to hindrance 

 of incasing structures is to remove the external parts and subject 

 the embryo to germinating conditions. 



Dr. Eckerson of this laboratory is making a study of the 

 internal changes that take place in the seeds of the hawthorn during 

 the process of after-ripening. The work is now well under way- 



Conclusions 



immediately 



more 



hyp 



than in the cotyledons or any of the external structures. 



