3 



can be made to grow at or below the freezing point, 

 and above that point, the degree of growth will be 

 always more or less influenced by that of tempera- 

 ture. Many seeds, however, will germinate as well 

 as ever after having been frozen, or having been 

 kept in frozen water. Although cold, therefore, 

 does not destroy the germinating faculty of seeds, 

 yet a certain degree of heat is essential to the dis- 

 play of it, and almost every species of seed seems 

 to require a degree peculiar to itself ; for each has 

 its peculiar season of germination, which season va- 

 ries with the temperature of the air. 



3. Light is another agent which has been suppo- 

 sed to possess a considerable influence in the germi- 

 nation of seeds. The experiments of Hooke, Scheele, 

 and Herschell, have established the distinction be- 

 tween the heating and illuminating powers of the 

 rays of light : and a third portion of these rays has 

 been supposed to enter more peculiarly into combi- 

 nation with various substances, and thence have ac- 

 quired the denomination of the Chemical Rays. Dr 

 Jngenhousz and M. Sennebier considered the presence 

 of light to impede the growth of seeds ; but the 

 Abbe Bertholin affirmed, that the difference in the 

 germination of seeds in the shade and in the light 

 was owing not to the light itself, but to the greater 

 evaporation of moisture which seeds exposed to the 

 light suffered : and he added, that if the seeds in 

 both cases were kept equally moist, those in the sun 

 germinated sooner than those in the shade. M. Sen- 

 nebier, however, repeated his experiments, and em- 

 ployed every precaution to ensure an equality of 

 moisture in both situations, and he constantly found 

 A2 



