PROOFS OF VITALITY. 35 



chemical affinity ; for as soon as the plant dies, this agent be- 

 gins to exert its power. The elaborated juices, no longer pre- 

 served by the vital principle, exert their mutual affinities, and 

 the whole plant in time is resolved into its original elements. 

 This power of resisting ordinary chemical laws, and of con- 

 trolling them in such a way as to make them subservient to 

 nutrition, evinces a peculiar vital energy, 



2. Gravity is constantly tending to bring the plant and its 

 juices to the earth ; but in opposition to this power the sap 

 ascends, and the plant or tree attains in some cases an eleva- 

 tion of more than one hundred feet from the surface of the 

 ground. A part of the matter which composes the tree is thus 

 carried up in opposition to gravity. It is true that it is car- 

 ried up slowly, and in small capillary tubes, in which mechan- 

 ical laws operate to some extent, still this will not wholly ac- 

 count for the fact. It requires vitality to effect its ascent. 



3. Heat and cold, two powerful agents of unorganized bo- 

 dies, are resisted by vegetables within certain limits. The 

 temperature of the juices of plants, and of their solid parts, 

 does not rise or fall with that of the surrounding medium. 

 The living vegetable will continue to flourish at a temperature 

 sufficiently high to produce disorganization after it is dead, 

 while the juices are said to circulate slowly during the cold 

 of winter ; for although the temperature of the juices is far be- 

 low the freezing point, they do not always congeal unless they 

 are taken from the tree. 



This power of resisting the extremes of heat and cold is 

 very striking in the case of some animals, which, when exposed 

 to a temperature of 300° F; or to — 80° F. retain constantly a 

 temperature at 9S or 100° F. Vegetables possess this proper- 

 ty in a less degree, but sufficiently to prove its existence. This 

 effect cannot be wholly* accounted for without supposing the 

 existence of a peculiar vital power. 



* The heat which is found in vegetables is partly due to chemical 

 changes. By the assimilation of the matter taken into the tree by the 



