58 BOTANICAL GAZETTE [july 



in their germination when removed from dry storage , light favoring 

 and darkness hindering germination. After 10 weeks of dry stor- 

 age, there was no germination in darkness at the optimum tempera- 

 ture, but after 39 weeks, 7-8 per cent germinated under the same 

 conditions. In light after 9 weeks of dry storage, 73 per cent 

 germinated under the same conditions. In a recent article (7) 

 covering a study of Stenotaphrum glabrum and Paspalum dilatatum, 

 Gassner found that P. dilatatum after-ripened in 1 to 2 weeks in 

 dry storage at 5o°-6o° C. 



The after-ripening of these seeds in dry storage is most interest- 

 ing, especially if it is a true case of after-ripening, that is if the 

 cause of delay lies in the embryo rather than in the coat. If the 

 delay were due to an impermeable coat, it would not be difficult 

 to understand how drying might cause it to rupture or change ' 

 otherwise its permeability to water or oxygen. The presence of 

 water is usually necessary to initiate chemical changes. This is 

 especially true for germination, and in the hawthorn, at least, is 

 also true for after-ripening, since neither the seeds kept dry for 

 long periods at the temperature of the laboratory nor at tem- 

 peratures most favorable for after-ripening showed any signs of 

 germination when placed under germinating conditions. 



The claim that certain seeds after-ripen in dry storage is quite 

 general. Kinzel (13) found that for oats kept in dry storage the 

 percentage of germination increased for 8 months after harvesting 

 and then gradually fell. But in all these cases there is need of a 

 thorough analytical study of the processes involved in the after- 

 ripening. 



Some general considerations 



The preceding tables indicate that the after-ripening in the 

 hawthorn takes place at low temperatures, the optimum for which 

 is 5 to 6° C. But the process goes on even at o° C, while at — 2 C. 



to — 3 C. it makes 



thawing, 



then, do not appear to be the ideal conditions for after-ripening. 

 The value of freezing and thawing to seeds which are lying in the 



the 



rupturing 



means of which water or oxygen are permitted to enter. Especially 



