396 TEXTBOOK OF BOTANY 



Table 13. Temperature and Length of Stratification Periods for Seeds to 

 Obtain the Best Yield of SeedHngs. 



^, , Most Effective Effective Time Required for 



r'lant rpi . lemperature t> ^ t> ix 



lemperature _,^ Best Results 



Range 



These results were secured under carefully controlled conditions. One 

 can hardly avoid wondering how long the dormant period of these seeds 

 may be in nature, and, if prolonged, what fraction of the embryos escapes 

 destruction by bacteria, fungi, and the innumerable animals near the soil 

 surface. Is it one in a million or one in a billion? 



Longevity of seeds. Present knowledge of how to shorten the period 

 of delayed germination of seeds gives some insight into the factors 

 involved in the presei'vation of seeds through a long period of time, 

 alive but ungerminated. Some seeds have greater longevity when rap- 

 idly dried in a desiccator and stored in sealed vessels or in an atmos- 

 phere of carbon dioxide. This is true even for seeds that survive but a 

 short time in nature where oxygen is abundant and the seeds are alter- 

 nately wet and dry. 



It has been clear for many years that lowering the temperature to near 

 the freezing point lengthens the period of vitality of most seeds. Sealed 

 storage of dry seeds at refrigerator temperatures apparently prolongs 

 the life of embryos still further and is now used by commercial seedmen. 

 A comparison of the results obtained with delphinium seeds emphasizes 



