SEED GERMINATION 235 



does not have to be at soil capacity for germination to occur. However, 

 the affinity of most seeds for water is insufficient to secure adequate 

 moisture for germination from soils of high osmotic concentration. 

 For this reason high concentrations of soluble fertilizers should not 

 be placed close to germinating seeds. 



Some seeds, such as red clover, possess hard, impervious coats which 

 do not allow water to pass. These seeds are frequently prepared for 

 germination by treatment with sulfuric acid, or they are blown 

 against needle points which scratch or puncture the outer coat. Treat- 

 ment with ZnClo in HCl (Cross and Bevan's solution), extraction 

 with fat solvents, and many other methods have been used to remove 

 obstacles to the penetration of water. 



Seeds respire during storage even though this process takes place at 

 a low rate. One of the factors which determines the rate of this 

 respiration is the moisture content of the resting seed. If seeds are 

 stored under conditions of relatively high humidity, their vitality may 

 be seriously impaired. The critical moisture content of stored seeds 

 depends on the temperature. As the temperature is lowered, the mois- 

 ture content can be increased without harmful effects. 



Temperature 



The optimal temperature range for the germination of seeds of most 

 agricultural plants seems to be from 68 to 86°F. Some seeds, such as 

 those of celery, bluegrass, and redtop, germinate better under certain 

 alterations of temperature than at constant temperatures. Most seeds 

 fail to germinate at temperatures as low as 32°F., although a period 

 of moist storage at temperatures of 35 to 55°F. results in better germi- 

 nation of many seeds. Low-temperature treatment of seeds often results 

 in a more rapid and vigorous growth of the seedlings. Although the 

 effect of such low-temperature treatment is well known, the reason 

 why a seed so treated will later germinate more rapidly and grow 

 better is not known. Temperatures as high as 110°F. prevent the 

 germination of most seeds. 



Oxygen 



Seeds have characteristic requirements as to the amount of oxygen 

 needed for germination. Most seeds germinate in the presence of air, 

 whereas others, such as those of cattails, germinate poorly or not at all 

 unless the oxygen supply is reduced. As a rule, any condition leading 

 to a lack of oxygen and an accumulation of carbon dioxide is harmful 

 to germination. In some cases the germination process is hindered 

 by the presence of a few hundredths of a part of carbon dioxide in 



