138 



BOTANICAL GAZETTE 



[ 



ARY 



time have been treated in some detail by Crocker (5). Seeds 

 that have dormant periods fall naturally into two groups : (1) seeds, 

 like certain members of the Leguminosae, have embryos capable 

 of immediate germination, but dormancy is here induced by asso- 

 ciated structures like the seed coats or pericarp; (2) the embryo 

 itself may be the cause of delayed germination. The second type 

 of dormancy may be due either to an immature embryo, as found in 

 Ceratozamia (4) and Ilex opaca (14), the former often being shed 

 at the time of or shortly after fertilization, while in the holly the 

 embryo is merely a globular undifferentiated group of cells at the 

 time of seed fall; or dormancy may appear in apparently fully 

 matured embryos, as is the case in some members of the Rosaceae. 

 The seeds of the sugar maple fall into the latter group, having 

 a dormant, morphologically mature embryo. 



Davis and Rose (7) found that in nature Crataegus mollis has 

 a dormant period of a year or more. This period of dormancy 

 can be shortened considerably by removing the carpel and testa. 

 It is doubtful whether any such interrelation exists between the 

 embryo of the sugar maple and its inclosing structures. 



The sugar maple sheds its fruit in the fall, after the first few hard 

 frosts. When given the most favorable conditions for germination 

 at time of fall the seeds fail to respond. The seeds must be kept 

 at a low temperature, with plenty of moisture present for a consider- 

 able period of time for after-ripening to reach completion. Under 

 natural conditions, if the seeds are kept moist during the fall and 

 winter, after-ripening will be complete the latter part of February 

 or early part of March. 



Investigation 



The object of the investigation was twofold: (1) to determine 

 the optimum temperature and water relations for after-ripening; 

 and (2) to determine the changes taking place within the embryo 

 during the after-ripening period. The fruit of the sugar maple 

 was collected the latter part of September and early part of October 

 direct from the trees in the Chicago region and northern Indiana. 

 Fruits were stored dry in wire baskets at various temperatures 

 from —5 to +30 C. ; others were stored in desiccators over water at 



