G2 SYL.VA AMERICANA. 



the seeds, which he helieves to he carried to a very great height, 

 though still escaping our instruments of observation. But this 

 mode of reasoning is, to say the least of it, still more inconse- 

 quential than the former ; because it is setting by a mere 

 probability from which nothing can be inferred, in opposition to a 

 direct fact, from which something surely should be inferred. It 

 may, indeed, be true, that the degree of heat impinging on the 

 surface of the seed is so great as to impede its germination ; but 

 as no direct proof can be adduced in support of the opinion, we 

 must just rest satisfied with the indications of our instruments, 

 till such time as other instruments shall be invented capable of 

 detecting their errors ; and with the previous conclusion, till such 

 time as some positive fact shall be opposed to the experiments 

 from which it is deduced. 



3. Action of Heat. A third condition necessary to germina- 

 tion is the access of heat. No seed has ever been known to 

 germinate at or below the freezing point. Hence seeds do not 

 germinate in winter, even though lodged in their proper soil. 

 But the vital principle is not necessarily destroyed in consequence 

 of this exposure ; for the seed will germinate still, on the return 

 of spring, when the ground has been again thawed, and the 

 temperature raised to a proper degree. But this degree varies 

 considerably in different species of seeds, as is obvious from 

 observing the times of their germination, whether in the same or 

 in different climates. For if seeds which naturally sow them- 

 selves, germinate, in different climates, at the same period ; or in 

 the same climate at different periods ; the temperature necessary 

 to their germination must of consequence be different. Now 

 these cases are constantly occurring and presenting themselves 

 to our notice ; and have also been made the subject of particular 

 observation. Adanson found that seeds which will germinate in 

 the space of twelve hours in an ordinary degree of heat, may be 

 made to germinate in the space of three hours, by exposing them 

 to a greater degree of heat ; and that seeds transported from the 

 climate of Paris to that of Senegal, have their periods of germi- 

 nation accelerated from one to three days. Upon the same 

 principle, seeds transported from a warmer to a colder climate, 



