ON THE STRUCTURE OP SEEDS. 361 



strengthened by the experiments of the French, chemists, 



whose applications may much more readily be supposed to 



correct and restore the albuminous juices, than to bring the 



dead to life. 



This idea of the albuminous matter, whether oily, muci- The albumen, 



laarinous, or farinaceous, being, when not a distinct and when " ot a « e " 

 ° > 7 o? parate body, 



separate body, always lodged in the cotyledons, throws ad- lodged in the 

 ditional light on the nature of the last mentioned parts, and Cotyledtta8 * 

 in a very beautiful manner confirms their analogy with leaves. 

 The discoveries of Mr. Knight have proved, that the nu- 

 tritious fluid or sap of plants is carried into the leaves, in 

 order to be there acted upon by air, light, heat, and mois- 

 ture. After these agents have produced their effects, the 

 fluids are sent back, through the returning vessels, into the 

 branch or stem, to furnish matter of increase to the whole 

 vegetable body. The chemical experiments, of Dr. Priest- 

 ley more especially, confirm this, by teaching us, that car- 

 bonic acid gas is absorbed by leaves in the day time through 

 their upper surface, and decomposed by them, its carbon be- 

 ing added to the sap, and its oxigen emitted by the under 

 surface. In the dark, leaves are found to absorb oxigen. 

 Let us apply all this to the germination of seeds. The ox- Chemical pro- 

 igen, known, as I have already said, to be necessary to this ^ t - in gerna " 

 process, being conveyed to the seed in its dark subterrane- 

 ous situation, is absorbed by its cotyledons, already stored, 

 from the constitution of the parent plant during their for- 

 mation, with albuminous matter abounding with the carbo- 

 nic principle. The chemical action of the oxigen on this 

 albuminous substance renders the latter a more or less sac- 

 charine, and, with the addition of the imbibed moisture, a 

 milky fluid, fit to be transmitted, through the returning ves- 

 sels of the cotyledons, into the stem of the embryo, espe- 

 cially as all these important parts have already begun to swell 

 by the absorption of moisture assisted by warmth. Hence we Light hurtful 

 see why light is found hurtful to incipient germination, and t " lucipie . at 

 why carbonic acid gas may be given out by seeds at that pe- 

 riod. We perceive also why the outside of seeds is so com- 

 monly dark coloured, or even black, as in canna, afzelia, 

 and others, it being the only part of the vegetable body, as 

 far as I recollect, that is ever positively black, except per- 

 haps 



