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time at length arrives when decay commences. The 

 wasted, enfeebled, and relaxed form gradually declines, ^ 

 until death finally closes all activity. The body then 

 becomes contracted and rigid; the skin exchanges the» 

 ruddy tinge of health for death's pallid hue. Decom-i 

 position speedily ensues, will all its offensive pheno- 

 mena ; and finally, the only permanent remains are* 

 the skeleton and a small amount of earthy matter. ' 

 The same characteristics attend the last period of 

 vegetable existence. Plants may flourish only for* 

 one season, or their hves may be extended through 

 centuries of years, yet decay eventually comes over 

 them ; becoming more and more stunted, weak, pallid, 

 and ragged, they eventually cease to live, become con- 

 tracted and rigid, and pass through the same phases 

 of putrefaction that are exhibited by the animal car- 

 cass. In both there was a time when warmth and 

 exposure to the atmosphere were the sources of 

 vigour — these now become the agents of destruction ; 

 they were once able to resist and to overcome the laws 

 of chemical affinity — they now are destroyed by their 

 attacks. What causes this most striking change ? 

 What antiseptic agent have they lost ? There can be 

 but one reply. It was their vitality. Now, let us 

 examine how the vitality of plants in other respects 

 resembles the vitality of animals, and we will confine 

 this examination to two or three points. 



Plants are excitable. Light acts upon them as a 



