SOCIETY OF CENTRAL ILLINOIS. 239 



sary for plant structure, with proper thermal conditions and a suffi- 

 ciency of suulip^ht, the circulation being free and unobstructed, we 

 have for the plant a state of health. If, however, there is a defi- 

 ciency of moisture, absence of the necessary heat and light, and the 

 inorganic elements wanting, the plant is in a weakened or enemic 

 condition, which is a form of disease. Or if the fluids are in super- 

 abundance so as to greatly engorge the vessels, then under great heat, 

 the delicate walls of the vessels burst asunder, the sap disorganizes, 

 sours, and we have the dread disease, blight. Or again, if under sim- 

 ilar conditions the circulation of the sap becomes morbid, natural 

 growth arrested, then we have various forms of morbid growth or 

 fungi. 



The germ theory, or bacterian theory, as the cause of disease 

 both in animals and plants, has receive large attention from many 

 eminent scientific men for a decade or more. The results of careful 

 microscopic examinations made by matter-of-fact men, have given 

 the theory many strong adherents. And 1 think it is generally con- 

 ceded that the millions of minute organisms that inhabit our atmos- 

 phere, have something to do in causing, and very much aggrav- 

 ating, many forms of disease. But with all the evidences revealed by 

 microscopic observations, the theory is not a fully-established hypo- 

 thesis as the cause of disease. My studies on this subject have forced 

 me to the conclusion that fungus, wherever it appears, and bacteria, 

 wherever they are found, are nearly always the consequence of and 

 not the cause of disease. 



Some years ago a paper was read before the Potomac Fruit 

 Frowers' Association, by John Brainerd, on "Pear Blight," in 

 which he gives some careful microscopic examinations of healthy 

 and blighted branches. He says the entire growth, near the blighted 

 portion, was green and vigorous, showing a continuous supply of 

 ascending sap, while the bark and alburnum in the blighted portion, 

 were dark and withered. From his examinations he concludes that 

 the newly- formed cells in the alburnum have, from some cause, 

 been ruptured, and the elaborated sap, destined for the support of 

 the plant, poured out into the interspaces of the cells, coagulated 

 and disorganized, producing, in the vegetable tissue, a condition 

 analagous to what is termed extravasation of blood in the animal 

 tissue. The microscopic appearance of the coagulated sap in the 

 blighted portion was most remarkable. Every vestige of cell for- 

 mation was destroyed, and nothing could be seen but a dark, coagu- 

 lated mass, pushed out through fissures in the bark, and this appear- 

 ance extended through the whole thickness of the alburnum, while 

 the sap-wood remained in a perfectly healthy state, conveying sap to 

 the unblighted portions above. This author, speaking of the causes 

 of cell-rupture, says that when the sap with which these cells are 

 always filled, is subjected to sudden expansion, from either high or 

 low temperature, the cell-walls become ruptured, and the sap, of 



