CH. IX.] UEATH AND DECOMPOSITION. 315 



bv Dr. Thomson, the Glasgow Regius Professor of 

 Chemistry. 



The poisonous substance is absorbed into the 

 plants system, and proves injmious when merely 

 applied to its branches or stem, almost as much as 

 if placed in contact with the roots. Ulcerations and 

 canker ai*e exasperated if lime be put upon the 

 wounds : and when Dr. Hales made 'a golden rennet 

 apple tree absorb a quart of camphorated spuits of 

 wine through one of its branches, one half of the 

 tree was destroyed. 



An uncongenial heat is as pernicious to vege- 

 tables as to animals. Every plant has a particular 

 temperatiuT, without which its functions cease, but 

 the majority of them luxuiiate most in a climate 

 of which the extreme temperatures do not much 

 exceed o'2'^ and 90°. No seed t,\tL1 vegetate, no sap 

 will circulate, at a temperature at or below the 

 freezing point of water, yet the juices of the plant are 

 not congealed even at a temperature fai' more de- 

 pressed, and I know of no other more satisfactory 

 proof, that like a cold-blooded animal, the frog and 

 the leech for example, it becomes torpid though life 

 is not extinct, imless excited by a genial temperature. 

 No cultivation will render plants, natives of the torrid 

 zone, capable of beaiing the rigoiu's of our ^^inters, 

 although their offsprmg raised from seed may be 



