19 1 2] ' DAVIS &• ROSE— AFTER-RIPENING 59 



is this true of seeds in which the cause of the delay is in the external 

 structures rather than in the embryo. In the hawthorn, freezing 

 and thawing undoubtedly bring about a splitting of the bony 

 carpels sooner than would otherwise occur, and in this manner 

 shorten the period of after-ripening. 



Temperatures alternating between that most favorable for 

 after-ripening, as 5 to 6° C, and temperatures ranging from 13 

 to 22 C. were not favorable to after-ripening. While we did not 

 employ other alternating temperatures than those above, we are 

 led to believe that there is always some favorable constant tem- 

 perature at which after-ripening will take place most readily, and 

 that any variation from this temperature either above or below 

 will retard it. 



There is considerable variation in the time in which individual 

 seeds after-ripen, as is indicated in table III and again in those seeds 

 that were removed from the cold too soon. In the latter case there 

 was always a large number of seeds that failed to germinate. These 

 in nearly all cases would germinate if the testas were removed, but 

 when not so treated and left at high temperatures, they would lie 

 upon the moist cotton for weeks without germinating. The higher 



to inhibit the Drocess of after-riDenine. The 



seem 



process of after-ripening then is interesting in that it does not obey 

 the van't Hoff temperature law for rate of chemical reactions, but 

 goes on faster at low temperatures. If this temperature law applies 

 to the individual metabolic processes involved in after-ripening, 

 it must apply to them with quite different coefficients, with the 

 general result that the process as a w T hole falls with a rise of 

 temperature. 



While the results with low oxygen pressure were mainly negative 

 or nearly so in all cases, we are not prepared to say that after- 



oxy 



sufficient 



certainly favors after-ripening. We ai 

 ments to determine more definitely the 

 to after-ripening and oxygen pressure. 



hawthorn 



seem 



to enter into the after-ripening of the 

 sat At the optimum temperature after- 



