440 THE AMERICAN NATURALIST [Vol. LV 



was found that a treatment of one and one half hours 

 would sufficiently char the seed coat to secure practically 

 100 per cent, of swelling (8). At first it seemed im- 

 possible to say whether this might not also injure the 

 embryos. Later it was discovered that whenever any 

 acid penetrated the cotyledons of dark blue plants they 

 turned pink. This color is probably due to the presence 

 of a chromogen similar to or identical with the one which 

 eventually produces the pink or blue flower pigments. 

 Since this color reaction is brought about by even faintly 

 acid solutions, it was thought that it would serve as an 

 effective check against overtreatment with the acid. 



After the preliminary experiments had shown the sul- 

 phuric acid method to be the best at our disposal a com- 

 plete series of tests were run on each of the 70 pedigrees 

 available for planting at that time. The dry seeds 

 were placed in the concentrated commercial acid and left 

 for 90 minutes. They were then washed rapidly through 

 several changes of sterile water until the water failed 

 to affect litmus paper after the seeds had stood in it for 

 20 to 30 minutes. It was found necessary to carry out 

 the washing rapidly since the weak acid readily pene- 

 trated into the cotyledons. 



After washing the seeds were subject to one of three 

 treatments. Some were left in sterile water until 

 sprouted. Others were removed as soon as they had 

 swelled. The great majority of the pedigrees swelled 

 within 18 hours. A few were completely swelled within 4 

 hours. In most cases they were left about 18 hours. A 

 third method was to transfer the seeds as soon as washed 

 to a nutrient solution. This did not show any advantage 

 over plain sterilized water. The seeds which were re- 

 moved from the water after washing and swelling were 

 placed on or between moist blotting papers. It was soon 

 found that those left in the water or placed between 

 papers kept wet and soggy excelled those which were 

 placed on papers merely kept moistened. Twenty-one 

 lots of seed failed to sprout at all, although the percent- 



