16 PBINCIPLES OF GAEDENING. [CH. I. 



scarcely occur also to those of the second and third 

 year, or even to those which were only a few weeks 

 later in their vegetation. 



It is not possible to enunciate a general rule 



I relative to germinating temperatures requiring no 

 exceptions, but in general, for the seeds of plants 

 natives of temperate latitudes, the best germinating 

 temperatiu'e is about 60° ; ^ for those of half-hardy 

 plants 70° ; and for those of tropical plants about 

 SO'^; and the necessity for such temperatui'es 

 depends upon the same causes that prevent the 

 incubation of eggs unless they be kept for a certain 

 period at a temperatui'e of about 100^. The 

 requisite changes are not produced either in the seed 

 or in the egg, miless it be submitted to the pro- 

 pitious temperature — but why this is requisite to 

 develope the forms, and effect the changes, without 



' wliich there is no vitality, is a secret at present 

 witlilield from man s understanding by the Almighty 



I architect, and w^e must rest satisfied with the 

 approximate Imowledge that heat is the vast and all 

 pen^ading agent he employs to call life into existence. 

 Although temperatm'es ranging between 60° and 

 80"^, are those most usually propitious to germina- 

 tion, yet a much higher temperature can be endured 

 by seed without its vitality being destroyed, and 



* Except where otherwise stated, Fahrenheit's thermometer is 

 referred to in the temperatures particularized. 



