SOCIETY OF CENTKAL ILLINOIS. 237 



HEALTH AXD DISEASE OF PLANTS. 

 BY DR. A. G. HUMPHREY, GALESBURG. 



The universe is governed by law. — Humboldt. 



All livino; forms, whether of plants or animals, have their peri- 

 ods of growth, maturity, decay and death. In studying the various 

 formations of our earth, science divides the time of their appearance 

 into epochs. During the Primordial epoch the Algse or Tangle for- 

 est and Polypi or Ascidia filled the primeval sea with the simplest 

 forms of vegetable and animal life. The Primary epoch clothed the 

 earth with fern forests and filled the sea with fishes. During the 

 Secondary epoch pine forests and reptiles appear. The Tertiary epoch 

 develops the leaf forests and mammals, and finally in the Quaternary 

 epoch we reach the era of man and cultivated forests. Each of 

 these periods of the development of living forms was governed by 

 the laws and forces peculiar to each of the geological epochs of the 

 world's organic history. The earth, with all its teeming life of veg- 

 etable and animal forms, originated and is now perpetuated under 

 undeviating inorganic and organic laws. All observable phenomena 

 are alike subject to law. The terrible and devastating tornado, the 

 gentle shower, the thundering cataract, the placid cascade, the cold 

 blasts of winter and the balmy days of summer, all exist and occur 

 in obedience to gravitation and electrical and climatic changes. The 

 science of chemistry in connection with geological research unfolds 

 the vast field of phenomena connected with the inorganic world. 

 Botany investigates those laws by which the vegetable life-principle 

 breaks up inorganic compounds and elaborates from inorganic mate- 

 rials the varied vegetable organisms that beautify and adorn the sur- 

 face of the earth. Physiology investigates all the phenomena 

 connected with animal life. Its province is to explain the wonder- 

 ful process of the vital force in elaborating out of vegetable bodies 

 the distinct parts of all animal organisms. 



Plants, like animals, are subject to the condition of health and 

 disease. Germination of seeds takes place in the dark, but the 

 essential condition for the life and health of plants is sunlight. 

 Without the wonderful organizing power of the great luminary of 

 day the vegetable kingdom could not exist. It may be asserted in 

 general that there are three essential conditions for the health and 

 growth of plants, viz: light, heat and moisture. These conditions 

 supplied in certain and regular quantities, the life, health, growth 

 and longevity of that plant is assured. If they are deficient, or are 

 supplied in superabundance, disease, dwarfing and premature decay 

 is the sure result. All plants depend directly on the inorganic ele- 

 ments for their nourishment. The vital laboratory of the ])lant 

 reduces inorganic compounds and arranges their elements into or- 



