" MYCOLOGICAL SECTION. 125 



PEAR BLIGHT. 



Micrococcus amylovorus Bur. 



By J. C. Arthur. 



No introductory description of the disease called Pear Blight, or Fire 

 Bliglit, is needed in order to distinguish it or call it to mind. For 

 nearly a century it lias been the most prolific theme for discussion by 

 horticultural writers and speakers amon^ the whole range of ])lant 

 maladies. Horticultural societies have talked themselves weary over 

 it, and editors of liorti cultural periodicals have found it necessary to 

 put a brake on tlie blight writers. The Western New York Horti- 

 cultural Society several years ago passed a resolution that the subject 

 should not be discussed in its meetings unless there were new facts 

 and additional information to be given. The acting president of the 

 American Poniological Society once cooled the ardor of discussion on 

 this subject by observing: "I confess I have nothing to say except 

 what is pure speculation, and I have got tired of speculation and of 

 hearing it on this subject.'' 



One need not be at a loss to account for this perennial activity. 

 The warm and repeated discussion which the subject has received is 

 evidence in itself, and corroborates the fact that the disease is a 

 serious evil, while tlie failure to reach conclusions that a majority 

 can subscribe to shows how obscure and beyond ordinary scrutiny 

 the cause lies, and how even to trace the external changes in the 

 course of the disease has taxed the full powers of observation. It 

 was with some apx^reciation of the intricate nature of the problem 

 that different societies at various times offered, or talked of offering, 

 prizes for the discovery of the cause of the disease and of a remedy. 

 They often contented themselves, however, with the appointment of 

 a committee from their own number, with instructions to study up 

 the matter and report at a subsequent meeting. The accompanying 

 map will show in a general way how wide an extent of country is af- 

 fected. It has been compiled from such data as could be gleaned 

 from horticultural journals and reports of horticultural societies. 



How the cause of blight was finally discovered by Prof. T. J. Bur- 

 rill, and additional verification worked out by the writer, need not 

 be narrated here ; it is much more to the point to state the results 

 and practical deductions, and leave the steps by which they have 

 been reached to be learned by reference to the original publications. 

 The cause of Pear Blight, as established by the last seven years of 

 research, is connected Avith the activity of germs., and the malady be- 

 longs to the category of germ diseases, now definitely proven to occur 

 both among animals and plants. The germs causing blight are of 

 extreme tenuity ; they are borne from place to place and from tree 

 to tree by the atmosphere, which is never so quiet but that its move- 

 ments are sufficient to keep such impalpable bodies afloat. Upon the 

 germs finding entrance to the juices of the plant the disease is set up 

 in a more or less virulent form. 



At the present time it is very well understood by all that bacterial 

 germs are in the greatest abundance everywhere, and we may Avell 

 inquire why all trees, at least all pear trees, are not speedily extermi- 

 nated. The chief safeguard from such a calamity is the fact that but 

 one specific kind of bacteria (named Micrococcus amylovorus Bur.) 

 is able to thrive in the tissues of the pear tree, and in consequence all 



