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CHAPTER XXI.
ON THE DISEASES OF PLANTS, PARTICULARLY AS ILLUSTRATIVE OF THEIR VITAL PRINCIPLE.
The diseases of Vegetables serve in many instances to prove their vitality, and to illustrate the nature of their constitution.
Plants are subject to Gangrene or Sphacelus, especially the more succulent kinds, of which a very curious account, concerning the Cactus coccinellifer, Indian Fig, or Nopal, extremely to our present purpose, is given by M. Thiery de Menonville, in his work on the culture of the Nopal as the food of the Cochineal insect. This writer travelled, about 20 years since, through the Spanish settlements in South America, chiefly noted for the cultivation of this precious insect, on purpose to transport it clandestinely to some of the
