102 CHYMiSTSlY APPLIED TO AGRICULTURE. 



. Ind>€speni'iiiQtly of t]ie light of the sun, without which 

 plants cannot flourish, vegetation requires a certain degree 

 of heat; buds generally do not begin to unfold till the at- 

 mosphere is at the temperature of from 50° to 54° : and 

 vegetation gains strength in proportion as the heat of the 

 atmosphere increases, provided that at the same time the 

 earth be sufficiently moist for the water to convey to the 

 plants the nourishment it contains, and to furnish to them 

 the means of transpiration. The influence of temperature 

 over vegetation is so marked, that we can see the latter di- 

 minish as the heat lessens, and resume its energies as that 

 is augmented. Warmth renders the sap fluid, and quick- 

 ens its circulation ; cold thickens it and renders it stag- 

 nant. If a right degree of atmospheric temperature, the 

 influence of the solar rays, or a suitable quantity of the 

 aqueous fluid be wanting, the growth of plants is retarded. 

 Thus we see it is not enough that plants are abundantly 

 supplied with nourishment ; it is necessary that the con- 

 coction of it should be favored by agents which concur in 

 causing its digestion. 



When the soil is too abundantly provided with manures, 

 especially of kinds that may be easily conveyed into plants 

 by water, their growth may be prodigiously increased ; but 

 if the digestive organs and the constant influence of the 

 sun do not concur in elaborating their juices, the result 

 will be, as I have before remarked, a kind of obesity ; and 

 none of the products will have either the savor or the odor 

 that they would have acquired if the nourishment had been 

 less abundant and better digested. It is not uncommon 

 for fruits and herbs to yield the odor peculiar to the ma- 

 nure with which they have been nourished, when it has 

 been too abundantly supplied. 



The juices circulate in plants, not only with the same 

 regularity of movement that we observe in animals more 

 perfectly organized, but with a degree of force sufficient to 

 carry them into all the organs, that they may receive in 

 each one of them a peculiar elaboration. 



The roots absorb fluids from the earth by means of their 

 capillary vessels ; but the force with which they are con- 

 veyed into the internal organs of the plant, and even into 

 the leaves, where their carbon combines with oxygen, is 

 superior to that of capillary attraction, and the weight of 

 the atmosphere. 



The celebrated Hales cut a branch of a vine four or five 



