178 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 



Uloth on the root of a maple seedling which penetrated a short dis- 

 tance into solid ice. Wheat has been known to germinate at the 

 freezing point. 



The following table, showing the effects of given temperatures upon 

 the germination of seeds, is taken from Nobbe's Haiidbuch der Samen- 

 kunde. The column under a indicates the number of seeds germi- 

 nated ; that under I shows the number of hours required to germinate 

 that number under the fixed temperature. 



PROPER CONDITIONS FOR TESTING SEEDS. 



The best temperature for the germination of most seeds is shown 

 to be 25 C. (77 F.), while for a few this optimum is 31 C. (88 F.) 

 and 37.5 C. (100 F.). But seeds germinating under natural condi- 

 tions seldom have the advantage of this optimum temperature. 



In testing seeds, therefore, since it is necessary to get as near the 

 natural conditions as possible, the temperature should be kept at 

 between 18 and 20 0. (64 and 68 F.). This has been found to be 

 the normal temperature for germination. Usually the heat of an 

 ordinary living room will be sufficient for home testing, but if the 

 temperature is likely to fall very low during the night it is better to 

 provide a little heat during that time. More harm will result from 

 a considerable decrease of temperature than from a slight increase. 

 In the European seed-control stations seeds are tested at a constant 

 temperature of 18 to 20 C. (64 to 08 F.). For grass seeds the 

 temperature is forced up to 30 C. (86 F.) during six hours of the 

 twenty-four, this variation in the heat being found advantageous. 



