316 Wisconsin State Horticultueal Society. 



strumeots such an inherent adaptation and power as to enable 

 them to perform their mighty mission with the precisioUj regu- 

 larity and force of law. 



These extreme views are now generally rejected, and there is a 

 strong tendency in the other direction, to regard these organisms 

 as the prime agents of disease and death, rather than the source 

 and promoters of life. The germ theory of disease has long been 

 held by a few, but of late years the number of its adherents has 

 greatly increased, and from being the cause of disease in a few 

 cases, it is now claimed to be the source of nearly all diseases, 

 both in the animal and vegetable world. Eecently it has 

 been declared that all the different forms of blight seen in our 

 apple and pear trees, and the yellows in the peach, are the direct 

 result of these germs. It is mainly on this account that the sub- 

 ject will be of interest to the horticulturist, and that some of 

 the most important facts brought to light by the scientific investi- 

 gation of these minute bodies are here given. 



Much has been discovered in regard to their history, but there 

 is still much that is unknown, and will doubtless long continue 

 so, for it is a significant fact that those who have spent the most 

 time and labor in these investigations seem to be the least 

 inclined to make positive statements in regard to them. "With 

 the data at command, it will not be possible, perhaps, to reach 

 definite results, but some benefit will be secured if a brief state- 

 ment of a few points in their history and of the difi'erences of 

 opinion held in regard to them, and the difficulties encountered 

 in their study, will serve to allay fears and check the disposition 

 to form hasty conclusions. 



The existence and active agency of those organisms in the 

 phenomena of life is not of recent discovery. As far as we have 

 any record of investigations made in the past, they seem to have 

 been first discovered by Leenwenhock, of Amsterdam, in 1675. 

 He was the inventor of the microscope, and while testing the 

 power of his lenses in the examination of a drop of stagnant rain- 

 water, he was greatly astonished to find that it contained a multi- 

 tude of atoms of globular form, darting about in every direction. 

 The following year he discovered them in fjeces, and in the tar- 



