2g2 



BOTANICAL GAZETTE 



[APRIL 



effect upon the hydrogen ion concentration. With samples lo and 

 II, 25 cc. of water were used, with samples 12 and 13, 50 cc, and 

 with samples 14 and 15, 100 cc. Although the variation of Ph is 

 considerable, it is by no means as great as that of the amount of 

 water used, nor is it in the same direction. That the degree of 

 dilution has no effect upon the Ph suggests the presence of buffer 

 salts, formed by the action of fatty acids produced during germina- 

 tion and the constituents of the ash already mentioned. 



After-ripened seeds similar to those used in samples 5 and 6, 

 which had failed to germinate when kept at room temperature for 

 10 days, gave a Ph corresponding very closely to that shown by 

 unafter-ripened seeds. This suggests that after-ripening is a 

 reversible process, a fact to which Crocker (5) has called attention, 

 and that a decrease in acidity may lead to secondary dormancy. 



TiTRATABLE ACID. — Determinations of the titratable acid were 

 made upon dry, after-ripened, and germinating seeds. For each 

 determination the seeds were ground in a mortar with 10 cc. of 

 water and titrated with N/io sodium hydroxide with pheno- 

 phthalein as an indicator. Titrations were made with freshly pre- 

 pared samples and with others which had been allowed to stand for 

 48 hours. To the latter were added 10 drops of toluol and o. 5 cc. 

 of N/io hydrochloric acid. Table VI shows the number of cubic 

 centimeters of N/io sodium hydroxide necessary to neutraUze the 

 free acid in each sample. The figures are the average of dupHcate 

 determinations. Corrections have been made for the acid added. 



TABLE VI 



While the amount of acid present is greatest in germinating 

 seeds, it is seen that after autodigesting 48 hours the greatest 

 percentage of increase over the freshly prepared samples is in seeds 

 well after-ripened. Here is shown the fact that the after-ripened 



