150 BOTANICAL GAZETTE [February 



in temperature no doubt introduces changes which may possibly 

 mask the real condition at the lower temperature. 



Accompanying after-ripening in the sugar maple is an increase 

 in the amount of free reducing sugars. Just how generally this 

 occurs in this type of embryo is still unknown. Whether increase 

 in amount of free reducing sugar is essential for the completion 

 of after-ripening is problematical. Dormancy is probably due 

 to a temporary suppression in the development of one factor or a 

 group of factors essential for the normal functioning of the embryo 

 in germination. It is impossible to select any one factor as the 

 cause of dormancy in the embryo of the sugar maple at the present 

 time. Whether any certain observed change in the embryo accom- 

 panying after-ripening is responsible for bringing dormancy to a 

 close, or whether this change results merely from the conditions 

 to which the embryo has been subjected, remains a question. 



Summary 

 River maple 



1. Seeds lose th6ir viability when the water content is reduced 

 to 30-34 per cent. 



2. Temperature seems to play no part in determining the critical 

 point of water loss. Higher temperatures only hasten the rate 

 at which the point of desiccation is attained. 



. 3. Respiratory activity in the desiccating seeds at 25 C. first 

 decreases slightly, then rises to a maximum, then gradually falls 

 to zero as desiccation progresses. 



4. After a slight initial increase, catalase activity gradually 

 decreases in the desiccating seeds. Catalase activity increases 

 enormously during the early stages of germination. 



5. Seeds of a river maple may be kept in a vigorous viable 

 condition for a considerable period of time at low temperatures 



C.) stored over water. 



6. There is a gradual decrease in peroxidase activity accom- 

 panying desiccation. 



Sugar maple 



I. Seeds after-ripen best at temperatures near 5 C, with a 

 £Ood supply of oxygen and moisture. 



