372 SCIENCE PROGRESS 



are not yet in a position to state definitely for any given plant 

 the factor or factors which bring about the phenomena observed. 



A comparative study of the conditions under which the seeds 

 of two closely related species of Acer will germinate has been 

 carried out by H. A. Jones (" Physiological Study of Maple 

 Seeds," Bot. Gaz.y Ixix, 1920, p. 127). Seeds of Acer saccharum 

 March and Acer saccharinum Linn, were chosen for investi- 

 gation because they show a striking contrast in season of 

 maturity, reaction to external conditions, chemical composi- 

 tion, and in their general physiological behaviour. The seeds 

 of the former are matured in the autumn and require a definite 

 period of after-ripening before germination can take place. 

 The optimum temperature for the after-ripening of these seeds 

 is approximately 5° C, and a free supply of oxygen and moisture 

 is essential. During the process of after-ripening an increase 

 in free reducing sugars, catalase activity and peroxidase activity 

 was observed. In the case of ^. saccharinum, on the other hand, 

 the seeds ripen in the spring and will germinate almost immedi- 

 ately upon a moist substratum, but lose their viability when 

 the water content is reduced to about 30 per cent. At low 

 temperatures, however, if stored over water these seeds retain 

 their viability for a considerable period. 



The germination of juniper seeds has always presented 

 many difficulties to nurserymen. In two recent papers D. A. 

 Pack (" After-ripening and Germination of Juniperus Seeds," 

 Bot. Gaz., Ixxi, 192 1, p. 32 ; " Chemistry of After-ripening, 

 Germination, and Seedling Development of Juniper Seeds," 

 Bot. Gaz., Ixxii, 1921, p. 139) presents the results of an exhaus- 

 tive study of this subject and shows that the seeds of Juniperus 

 germinate readily after being maintained at a constant tem- 

 perature of 5°C. for about 100 days to allow for the after- 

 ripening of the dormant embryo. Accompanying after-ripening 

 the following changes, amongst others, were observed : (i) An 

 increase in the hydrogen-ion concentration of the embryo ; 

 (2) an increase in titratable acid ; (3) a decrease in the amount 

 of stored fat and protein ; (4) an increase of sugar content ; 



(5) the translocation of fat from the endosperm to the embryo ; 



(6) a slight increase in the rate of respiration ; (7) an increase 

 in the value of the respiratory quotient ; and (8) a marked 

 increase of catalase activity. The optimum temperature for 

 the germination of Juniperus seeds was also found to be 5° C. 

 In the course of this investigation it was discovered that 

 when the seeds which had completed their after-ripening 

 processes at 5° C. were transferred to temperatures above 

 15° C. they! were thrown into a state of secondary dormancy. 



A satisfactory solution of the problem as to why the seeds 

 of annual plants germinate in the spring after lying dormant 



