100 



GROWTH OF PLANTS 



tained in germinators at various temperatures. At the optimum tempera- 

 ture for after-ripening (1° C, 34° F), except for a slight initial drop, there 

 is a continuous rise until at the completion of the after-ripening, after 



control I 



5 7 



WEEKS OF 



9 II 



STRATIFICATION 



Figure 36. The catalase activities of Sorbus aucuparia seeds stratified for periods of 

 1 to 15 weeks at various temperatures. 



12 weeks, the catalase has increased 5-fold. At the somewhat higher and 

 variable temperature of the icebox, which is also a poorer temperature for 

 after-ripening, it rose 12-fold in nine weeks. The catalase also rose faster 

 at 5° C (41° F) than it did at the optimum after-ripening temperature. At 



