SECT. I. EXCITABILITY. 439 



to the acknowledged laws of chemical affinity, 

 which, as soon as the vital principle is extinct, 

 begin immediately to give indication of their action 

 in the incipient symptoms of the putrefaction of 

 the dead body. 



But the rule is also applicable to the case of ve- Applied to 

 getables, as is proved by the intro-suseeption, di- V 

 gestion, and assimilation of the food necessary to 

 their developernent ; all indicating the agency of a 

 principle capable of counteracting the laws of che- 

 mical affinity ; which, at the period of what is 

 usually called the death of the plant, begin also 

 immediately to act, and to give evidence of their 

 action in the incipient symptoms of the putrefac- 

 tion of the vegetable. Vegetables are therefore 

 obviously endowed with a species of vitality. But 

 admitting the presence and agency of a vital prin- 

 ciple inherent in the vegetable subject, what are 

 the peculiar properties by which this principle is 

 characterized? 



SECTION I. 

 Excitability. 



ONE of the most distinguishable properties of 

 the vital principle of vegetables is that of its ex- 

 citability, or capacity of being acted upon by the 

 application of natural stimuli) impelling it to the 

 exertion of its vegetative powers; the natural 

 stimuli thus impelling it being light and heat. 



*V\ 



OF THE 



(i UNIVERSITY ) 



