1886.] NATURAL SCIENCES OP PHILADELPHIA. 329 



attention of the scientific world. Although this was now the 

 popular hypothesis, it cannot be said to have received more sub- 

 stantial credence than those which had gone before, either from 

 the horticulturists or the scientists. The experimental results 

 gained b}^ Prof. Burrill were confirmed and extended by the 

 writer ^ during 1884, by means of a similar series of inoculations. 



Of the multitude of minor hypotheses which were put forth in 

 explanation of phenomena connected with pear-blight, and which 

 were variously received, and of all degrees of plausibilit}^, it is 

 Impossible to speak at this time without carrying this paper to 

 undue length. 



Beginning of Experimental Research. The question of the 

 cause of pear-blight was finally removed from the domain of 

 speculation to that of established fact by a series of crucial 

 experiments performed by the writer ^ a year ago, and recorded 

 in a paper before the American Association at the Ann Arbor 

 meeting. These consisted in showing that the bacteria when 

 removed from the tree and passed through a series of artificial 

 cultures would generate the disease when again introduced into 

 the tree, and that the juices accompanying blight when cleared 

 of bacteria by filtration will not produce the disease. 



Having now come to a firm basis for scientific advancement, let 

 us look over the historical ground again to see if some one did 

 not hit upon the true explanation of the disease, although he may 

 not have been aware of its sisfnificance. In a connection like 

 this, facts derived from experiment have greater weight than 

 statements of opinion ; the latter acquire importance in propor- 

 tion as the}'^ are logically derived from correct and close observa- 

 tion. Bearing this in mind, we need not give much heed to the 

 not uncommon inference that pear-blight was in some way inti- 

 mately related to the epidemic diseases of man, e. g. cholera. 

 This view is said to have been quite frequently entertained in the 

 early part of the century, but was not sanctioned by the learned. 

 The. use of such phrases as " first cousin to the cholera," " a spe- 

 cies of vegetable ferment," etc., surely does not entitle the author 

 to any priority in way of discovery. 



1 Rep. N. Y. Agric. Exper. Station for 1884, p. 357. 



^ Proc. Am. Assoc. Adv. Sci., vol. xxxiv, 1885, p. 295 ; Bot. Gazette, vol. 

 X, 1885, p. 343 ; Gardeners' Chronicle, vol. xxiv. 1885, p. 586. 



22 



