Physiologie. 249 



temperature of the greenhouse, the high temperature either stops 

 or greatly retards the proccss of after-ripening. 



If the seeds are completely ai'ter-ripened and removed from the 

 cold to the temperature of the greenhouse, they germinate very 

 quickly. The high temperature greatly stimulates the process ol 

 germination. 



After-ripening readily takes place under ordinary oxygen pres- 

 sure, but it has not been füll}'- determined to what extent the oxygen 

 pressure ma}'- be reduced and the process still go on. 



The pulp, carpels, and seed coat itself tend to delay the process 

 of after-ripening, probably b}'- preventing the free access of water. 

 The changes that take place in the embryo during the after-ripening 

 are not yet known. 



Seeds treated dry as well as those treated under water did 

 not after-ripen. 



While after-ripening and germination in the hawthorn is a 

 continuous process, that is, we cannot teil where one leaves off 

 and the other begins, the Optimum temperature for the latter is 

 considerably above the Optimum for the former. Jongmans. 



Eckerson, S., A physiological and chemical study ot 

 after-ripening. Contributions from the Hüll Bot anical 

 Laboratory 170. (Bot. Gazette. LV. p. 286—299. 1913.) 



This paper contains a preliminary microchemical study of the 

 chemical changes during after-ripening. The investigations were 

 made on different species of Crataegus. The results form the basis 

 for a quantitative study. This paper gives the results of the micro- 

 chemical study, together with quantitative determinations of the 

 substances in the embryo at different periods during after-ripening. 



At the end of the paper one finds foilowing summary of the 

 results. 



Condition of the embryo in dry storage. Food is stored in the 

 embryo in the form of fatty oil; there is also considerable licithin; 

 neither starch nor sugar is present. The reaction of the cotyledons 

 is acid, but the hypocotyl is slightly basic. The water-absorbing 

 power of the hypocotyl is less than 25 per cent of the wet weight. 



There is a series of metabolic changes in the embryo during 

 the period of after-ripening. The initial change seems to be an 

 increased acidity. Correlated with this is an increased water-holding 

 power, and an increase in the activity of catalase and peroxidase. 



Near the end of the period of after-ripening there is a sudden 

 increase in the acidity, and in the water content; here oxidase 

 first appears. All of these increase until the hypocotyl is 3—5 cm. 

 long. At this time the fats decrease and sugar appears. Hydrocyanic 

 acid is present in the cotyledons. 



The after-ripening period can be greatly shortened by treating 

 the embryos with dilute acids, HCl, butyric, and acetic. The water- 

 holding power, the acidity, and the amount of peroxidase increase 

 much more rapidly, and oxidase appears much earlier, than in un- 

 treated embryos. 



It is evident that there is a correlation between acidity of the 

 hypocotyl of Crataegus, its water-absorbing power, production of 

 enzymes, and germinating power. Whether the acidity is causal or 

 merely correlative is not known. There is some evidence, however, 

 that it is causal. Green has shown that it leads to the liberation 



