CHANGES PRODUCED BY N0tJRi3HAI£NT. Idi 



The germination of seeds and ti^^ fjivtjlliqgi pf 1:)|i^cis»,ifi' 

 the spring, are almost entirely the results of physical laws : 

 ■oxygen is the only agent necessary to produce them : wa- 

 ter and heat are necessary auxiliaries, but they do not in 

 any way enter into the new combinations ; they only facili- 

 tate the changes that are going on. The oxygen unites 

 with carbon to form carbonic acid gas ; by this means the 

 mucilage and starch . are reduced to the state of a milky 

 liquor, which serves as the first aliment of the young plant 

 or twig. 



As soon as the plant has unfolded its leaves, or the radi- 

 cles of the seed have penetrated into the soil, the system 

 of nourishment is changed : every part of the plant in con- 

 tact with the atmosphere gives out carbon during the 

 night, or when in darkness ; but the carbonic acid which 

 this forms with oxygen, instead of remaining in the air, as 

 at the period of germination, is absorbed principally by 

 the roots and leaves, and decomposed in the last by the 

 solar rays; the carbon remaining fixed in the plant, whilst 

 the oxygen is exhaled in the form of a gas. Plants are 

 likewise nourished by that aqueous fluid which, constantly 

 existing in the atmosphere in greater or less abundance, is, 

 by the diminished temperature of the air during the night, 

 deposited in the form of dew. The water contained in 

 the soil dissolves the juices of the manures, and transmits 

 them to the plants. 



But in order that plants should flourish, it is not suffi- 

 cient that they have at their disposition all their necessary 

 aliments ; it is further requisite, that the elaboration of 

 these be favored by other causes possessing equal influ- 

 «nce over vegetation. 



I have already remarked, that leaves do not transpire 

 oxygen excepting when exposed to the rays of the sun ; so 

 that the carbonic acid remains in the plant during the 

 whole time that the solar rays are hidden. The establiglir 

 ment of this fact enables us to explain many of the most 

 important phenomena of vegetation : we learn from it, why 

 plants that grow in the shade never produce fruits having 

 the same taste, perfume, or texture as those borne by 

 plants of the same kind growing in the sun ; and why the 

 various sorts of fodder and green herbs are of bad quality, 

 when the sun has not access to them to facilitate th« 

 decomposition of carbonic acid and the elaboration of the 

 nutritive fluids. 

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