1886.] NATURAL SCIENCES OP JPHILADELPHIA. 33l 



Another interesting experiment was performed by Dr. E. S. 

 Hull,^ of Illinois, in 1868. Having received some blighted apple 

 twigs from a correspondent, he cut pieces from them with which 

 he " inoculated several succulent pear shoots by tying in the pieces 

 as in budding." This was done the middle of June, and no ob- 

 servation taken for thirty-four days, when the blight was found 

 to have extended several inches into the healthy tissues. From 

 this he very justly concludes that the blight in apples and pears 

 is but one disease, but seems to take it for granted that in both 

 it is due to " vitiated sap." 



The fact that the disease may be transferred to healthy trees 

 by the pruning knife has been observed by several persons. H. 

 Wendell,^ of New York, says in 1849, "I am also careful that the 

 blade of the knife is perfectly clean, and that it has none of the 

 sap of a diseased tree adhering to it, because I have known many 

 valuable trees destroyed by having been inoculated in this man- 

 ner." Prof. Turner,^ of Illinois, makes a similar statement : " I 

 found that this disease is exceedingly contagious, for if I used 

 my knife to prune a healthy tree after having used it in shaving 

 the diseased one, I communicated the disease to that tree." 



Prof. Burrill first observed the bacteria of blight in 1877,^ 

 but did not recognize them as such till the following year,^ when 

 he avowed his belief that they were the cause of the disease. 

 His first inoculation experiments were made in 1880, as already 

 stated. In 1882 he characterized the organism under the name 

 of 3Iicrococcus amylovorus.^ 



Description of Micrococcus amylovorus Bur. The form of 

 this species of bacteria is very constant, under all conditions. 

 The single cells are from oval to roundish-ovoid, and only vary 

 by slight changes in the ratio between their length and breadth 



1 Trans. 111. Hort. Soc. for 1868, p. 320. 



2 U. S. Patent Office Rep. for 1849, pt. 11, p. 446. 



3 Trans. 111. Hort. Soc. for 1878, p. 81. 

 * Same for 1877, page 114. 



^ Same for 1878, page 79. 



^ The Bacteria (a reprint from Rep. of 111. Industrial Univ. for 1882), 

 p. 42 ; Amer. Naturalist, vol. vii, 1883, p. 319. In the last publication, 

 by a typographical error, tiie name was made to read M. amylivorus, a 

 mistake wliich has been copied into other works see Grove's Bacteria 

 and Yeast Fungi, London, 1884, p. 10. 



