SECT. I. CONDITIONS. 



is too much, it then rots. The case is not the 

 same, however, with all seeds. Some can bear but 

 little moisture, though others will germinate even 

 when partially immersed ; as was proved by an 

 experiment of Du Hamel's, at least in the case of 

 Peas, which he placed merely upon a piece of wet 

 sponge, so as to immerse them by nearly the one 

 half, and which germinated as if placed in the soil. 

 But this was found to be the most they could bear ; 

 for when totally immersed in the water they rotted.* 

 There are some seeds, however, that will germinate S 

 even when wholly submersed. The seeds of Aqua- 

 tics must of necessity germinate under water ; and 

 Peas have been also known to do so under certain 

 conditions. 



SUBSECTION V. 



Access of Atmospheric Air. A fifth condition No gernu- 



.... r nation in 



necessary to germination, is the access of atmos- vacuo . 

 pheric air. Seeds will not germinate if placed in 

 a vacuum. Ray introduced some grains of Lettuce 

 seed into the receiver of an air-pump, which he 

 then exhausted. The seeds did not germinate. 

 But they germinated upon the re-admission of the 

 air, which is thus proved by consequence to be ne- 

 cessary to their germination.-)' 



The experiments of Homberg do indeed seem 

 to militate somewhat against this conclusion. They 

 are recorded in the Memoirs of the French Aca- 

 * Phys. des Arb. liv. ii. chap. viii. + Phil. Trans. No. xiii. 



