340 



nutrient matter is carried info plants, and in the opinion of some, is even 

 reduced in them to a solid form, and applied to the purposes of nutrition. 

 — See Ellis, Veget. Physiol, in Suppl. Encyclop; Britan. 



Notwithstanding what is here said in the text, respecting light as a 

 condition of internal development peculiar to plants, it may be doubted, 

 whether it be not nearly as necessary to animals. Cattle will not fatten 

 so well, when stallfed or shut up, as in good ground, and in fine weather, 

 with the free enjoyment of light. Light is caloric ; and the difference 

 between night and day in this respect is extremely curious. The sub- 

 stratum of ground, on which beasts feed, as affected by caloric, is a 

 subject which deserves greater chemical and physiological inrestigation 

 than has as yet been bestowed upon it. 



Note IV. Page 100. 



It has been doubted, by some phytologists, whether trees generate 

 heat. I believe it is certain, notwithstanding what is cursorily stated in 

 the text, that frosts of very extraordinary severity will destroy trees. 

 The non-conducting property of wood may in some measure protect the 

 juices ; but their chemical composition, as here stated, is such, that they 

 do not congeal, unless the cold be of the severest sort, and many 

 degrees below the freezing point of water. In weather so hard as to 

 occasion the juices to freeze, the wood, in the act of congelation, is 

 violently rent asunder : but in the more common destruction of woody 

 plants, it is not so much the degree of cold that kills them, as the too 

 sudden reapplication of heat. 



The ingenious Hassenfratz, to whom the chemical world is under 

 some obligations, held, that vegetables are not fed by carbonic acid. 

 In a Memoir on the Nourishment of Vegetables, read in 1792, to the 

 Royal Academy of Paris, having shown, as he conceived, that water 

 and air are insufficient for all the purposes of vegetation, he attempted 

 in a second ingenious paper to prove, that carbonic acid gas is not de- 

 composed and digested in the organs of growing vegetables, and that 

 they cannot be fed by it ; because oxygen, escaping from combination 

 in the decomposition of carbonic acid, and water escaping in vapour in 

 the state of gas, would absorb caloric, and j)roduce cold : whereas, by 

 the experiments of the late John Hunter, living vegetables contain a 

 degree of heat greater than that of the surrounding atmosphere. The 

 reason of this difference in opinion between these two accurate; in- 

 quirers may possibly be, that Hunter's experiments were made only in 



