APPENDIX A. 



Abstract from paper of Prof. J. C. Arthur on " Pear Blight :" 



The experiments on which the address was based have been carried 

 on at the Agricnltuial Experiment Station at Geneva, N. Y., during 

 the last two years. The first work in this line of investigation was 

 done by Prof. Burrill of Illinois, who showed by many experiments 

 that the disease may be introduced into healthy branches of the pear- 

 tree by transferring a minute particle of diseased tissue or the viscid 

 substance accompanying the disease to the healthy branch. He also 

 found that germs or bacteria were an invariable accompaniment of the 

 disease. The experiments at Geneva corroborated this. 



The inoculation was soon found to be as certainly conveyed when a 

 drop of water was used which had been in contact with diseased pear 

 wood and had taken up some of the germs as when the exudation or 

 diseased tissues were used. The disease so introduced in healthy 

 tissues showed itself by the blackening of the bark in about a week on 

 an average. It was found to grow the best in the most succulent 

 tissues, such as the tips of young shoots, and especially in unripe fruit. 

 It progresses through the limbs most rapidly in the warmest weather 

 but is not killed by cold, being able to make a slow growth all winter. 



Mode of Attack — Experiments to learn the manner in which the 

 germs enter the pear-tree were at first unsuccessful. Diseased 

 branches tied into a tree of healthy growth did not communicate the 

 disease. Apparatus an-anged to draw air across diseased branches 

 and then over healthy ones, gave no results. A potted pear-tree was 

 wateied for over a month only with water filled with the germs of the 

 disease and still remained healthy. An arrangement to permit a slow 

 dripping of water containing the germs upon very young pear growth 

 did, however, succeed in conveying the disease to healthy tissues. It 

 was observed the present spring that an English hawthorn had 

 blighted badly. The short spurs on the sides of the limbs bear 

 clusters of flowers and it was observed that these flowers on the 

 blighted limbs had made no growth since the time of opening, 

 although it was the latter part of June and the unblighted limbs had 

 the fruit two-thirds grown. The germs of the disease had evidently 

 entered through the flowers a full month previous, and had only 

 recently been conspicuous by the dying of the leaves. But many of 

 the twigs were dead where there were no flowers ; here the germs had 

 evidently entered through the tenderest tissue of the growing tip and 

 progressed downward, as was shown by the end leaves being dryest 

 and apparently longest dead. 



Growth of the Germs Outside of the Tree — It had now been shown 



