328 PROCEEDINGS OF THE ACADEMY OF [1886. 



it was independently elaborated by A. J. Downing' in Ms work 

 on Fruits and Fruit-trees of America, who first called it the 

 frozen-sap theory, and who is usually spoken of as the author of 

 it. This view has probably had more firm adherents than any 

 other, as it explained many phenomena connected with the dis- 

 ease in a fairly satisfactory manner. It was especially well 

 received in the western States. 



The next hypothesis which gained the attention of the public 

 was the fungus theory. Its first successful presentation was in 

 1863 by Dr. J. H. Salisbury ,2 who figured the fungus which he 

 decided to be the specific cause of this kind of blight, and ven- 

 tured to give it a name, although he was sadly in error in most that 

 he did. Thomas Meehan,^ editor of the " Gardener's Monthly," 

 has ably championed this explanation, and done much to keep it 

 in favor. In 1875, Dr. J. G. Hunt,* by Mr. Meehan's request, 

 undertook a microscopical examination of blighted pear-twigs, 

 and confirmed the opinion that it was due to a fungus, without, 

 however, deciding upon the specific character of it. 



Blighted trees often attract attention immediately after a 

 thunder storm, and from this and other circumstances the belief 

 that the malady is due to electricity has gained many adherents, 

 but the argument has not had a full and connected presentation. 



The last hypothesis of historical importance is the bacterial 

 theory. Although hinted at by a number of horticultural writers, 

 yet the credit of it is due to Prof. T. J. Burrill,^ who in 1878 dis- 

 tinctly stated his belief that the cause resides with the bacteria 

 which he found in great abundance in the tissues of afiected 

 branches. In 1880 he performed a series of experiments^ by 

 inoculating healthy branches with the juices of diseased ones, the 

 results of which were presented to the American Association at 

 its Boston meeting, thus first bringing the subject clearly to the 



Fruits and Fruit-trees of America, p. 594 ; same, 2d Revision by Chas. 

 Downing, p. 646. 



=* Ohio Agric. Rep. for 1863, p. 450. 



^Proc. Amer. Pomol. Soc. for 1867, p. 59 ; and elsewhere. 



* Gardener's Monthly, vol. xvii, 1875, p. 245. 



^ Trans. 111. Hort. Soc. for 1878, p. 80. 



" Proc. Amer. Assoc. Adv. Sci., vol. xxix, 1880, p. 583 ; Rep. of 111. 

 Industrial Univ., for 1880, p. 62 ; Trans. 111. Hort. Soc. for 1880, p. 157 ; 

 Amer. Naturalist, vol. xv, 1881, p. 527. 



