26 CHEMICAL PHENOMENA OF VEGETATION. 



GERMINATION. 



We have ascertained that a seed, considered with reference to its 

 organization, consists, 1st. of an embryo which includes the germs 

 of the root and of the stem; and 2d. of the cotyledon, or cotyledons. 

 Considered with reference to their chemical compositions, seeds ex- 

 hibit a certain similarity of constitution. They contain : 1st. starch 

 and gum ; 2d. a highly azotized matter analogous to the caseum of 

 milk and animal albumen ; this is the matter which is commonly and 

 very improperly designated under the name of gluten, and of vegeta- 

 ble albumen ; 3d. a fatty or oily matter, rich in carbon and hydrogen. 

 Seeds contain either fixed oils, such as hemp-seed, rape-seed, &c., 

 or volatile oils, as aniseed, cmnmin-seed, &c. The different prin- 

 ciples which are associated in the seeds vary considerably in their 

 relative proportions : they also vary slightly in their nature. One 

 seed, that of the colewort, for example, will contain more than forty 

 per cent, of its weight of oily matter, while another, such as wheat, 

 will only contain a few hundredths. Oats may contain ten or twelve 

 per cent, of caseum or gluten ; in certain varieties of wheat, 

 analysis indicates a much larger quantity. The proportions of starch, 

 gum, sugar, or mucilage do not vary less. It almost always hap- 

 pens that these different substances are found associated in the same 

 seed ; sometimes one predominates and the others only enter in very 

 small proportion. 



After burning, the ashes of seeds are always found composed of 

 phosphates, sulphates, and alkaline and earthy chlorides. These 

 ashes also contain silica, and certain carbonates produced by the 

 destruction of salts formed by organic acids. 



If some seeds, sufficiently moistened, are placed under a bell- 

 glass containing atmospheric air confined over quicksilver, all the 

 signs of germination will soon be perceived. In the course of a few 

 days, provided the temperature has been sufficiently high, germina- 

 tion will have made a certain progress. Supposing that the tem- 

 perature of the bell-glass has not varied, and that the atmospheric 

 pressure remains the same, we generally find that the air, in which 

 germination has been proceeding, has not changed its original vol- 

 ume ; but it has been modified in its composition : a notable quantity 

 of carbonic acid has been formed, and a portion of oxygen has dis- 

 appeared. The volume of carbonic acid produced, represents for the 

 most part the volume of oxygen which has disappeared. Now we 

 know that carbon being burnt in a certain volume of oxygen gas, 

 produces sensibly an equal volume of carbonic acid gas. It was the 

 knowledge of this fact that induced M. de Saussure to say, that in 

 germination, carbonic acid is produced by the combustion of a por- 

 tion of the carbon which enters into the composition of the seed. 



Germination and the appearance of carbonic acid, (which is al- 

 ways its consequence,) take place as readily in pure oxygen gas, as 

 in atmospheric air; but if placed in an atmosphere deprived of oxy- 

 gen, seeds cease to germinate. Consequently, germination is out of 

 the question in azote, in hydrogen, or in carbonic acid, however fa- 



