i 4 8 BOTANICAL GAZETTE 



FKURLARV 



Recent studies have thrown considerable light upon the behavior 

 of seeds that require a definite time under certain favorable condi- 

 tions to after-ripen a morphologically mature embryo. The major 

 portion of the work up to the present time has been done upon 

 various members of the Roseceae. No doubt seeds of this general 

 behavior exist in many more of our plant families, especially among 

 the uncultivated forms. Not until more work has been done upon 

 a wider range of plants will it be known just how widespread this 

 phenomenon is. The few species studied thus far by various 

 investigators show remarkable similarity of behavior in several 

 features accompanying after-ripening. There are five more or 

 less specific changes, according to Crocker and Harrington (6), 

 which are quite conspicuous in the constant way which they seem 

 to accompany after-ripening in seeds of this type: (i) rise in vigor 

 of seedling, (2) increase in amount of water absorbed, (3) increase 

 in total acidity, (4) increase in catalase, and (5) oxidase activity. 



When after-ripening is accomplished under the most favorable 

 conditions of oxygen pressure, water relations, and temperature, 

 seedling vigor is in all cases at its maximum. In the sugar maple, 

 at least, seedling vigor can be judged only during the first stages 

 of germination after the completion of the period of after-ripening. 

 After-ripening, however, may complete itself under conditions not 

 favorable for the greatest expression of seedling vigor. 



Rose found slight increase in acidity accompanying after- 

 ripening in the seeds of Tilia. This was correlated with greater 

 water holding capacity. In the haw (11) delayed germination of 

 the embryo has been found to be due to a dormant hypocotyl. 

 In the dormant seed this organ is slightly alkaline or neutral, but 

 with after-ripening the hypocotyl becomes distinctly acid. Accom- 

 panying this increased acidity there is increased water holding 

 capacity of the hypocotyl, along with increased activity of the 

 enzymes. Here the hydrophilous colloids have a greater water 

 holding capacity in a slightly acid medium. When the entire seed 

 of the haw is considered, however, we find a slightly higher water 

 holding capacity in the dormant than in the after-ripened seed. 

 In the sugar maple the water holding power of the hypocotyl only 

 was not determined. Considering the hydrogen ion concentration 



