248 HERMETICAL ENCLOSURES BAD. 



unless the exposure is very much prolonged ; nor have we any 

 evidence to show that it does, so long as they remain dry. The 

 way in which the atmosphere would act injuriously upon dor- 

 mant seeds is, by its oxygen abstracting their carbon ; and it 

 was formerly supposed that the carbonic acid extricated by 

 germinating seeds was formed in this way. But the very valu- 

 able observations and experiments of Messrs. Edwards and 

 Colin (See Comptes rendms de I'Academie des Sciences, vii. 933) 

 show that carbonic acid is formed by the assistance of the 

 oxygen obtained by the decomposition of water. 



Chemists may question tlie sufficiency of this explanation ; but, at all 

 events, it wiU not be denied that the preservation of vitality in seeds 

 depends upon preserving the stability of the chemical compounds of 

 which they consist. This we believe to be the hinge upon which every- 

 thing turns. Before a seed is quite ripe its elements are highly unstable 

 or liable to change, and the least alteration in the conditions to which 

 they may be exposed will cause it either to germinate or perish, as is 

 seen in Oranges and Cucumbers, whose seeds will often germinate while 

 hidden within the fruit that bears them. But when a seed is perfectly 

 ripe its elements become comparatively stable or indisposed to change, 

 and to induce germination is in proportion difficult, while those altera- 

 tions which are succeeded by death are slow in taking effect. 



If we apply these considerations to the plans .usually em- 

 ployed for preserving artificially the vitality of seeds, we shall 

 find them offer an explanation of the success that attends some 

 methods of packing, and the failure of others. 



The great object of those who have devised means of packing 

 seeds for distant journeys has, in general, been to exclude the 

 air, and all other considerations have been subordinate to this. 

 Enclosure in bottles hermetically sealed, in papers thickly 

 coated with wax, in tin boxes, and similar contrivances, have, 

 therefore, been resorted to : but no advantage can be derived 

 from excluding the air, and the disadvantage is very great ; 

 for the effect of excluding the air is to include whatever free 

 moisture seeds may contain or he surrounded by ; this mois- 

 ture is sufficient, in high temperatures, to excite germination, 

 which, when it cannot be continued, inevitably ends in a decay 

 of the tissue, especially of the seed coats, which have no vitality 

 themselves, and the embryo perishes. 



