Pear-blight is caused by a bacterium, _Bacillus amylovorous_, the discovery of which by Burrill in 1877 as a cause of this disease is one of the landmarks in plant pathology. The organisms are dormant during the winter, which they pass in the margins of blight-cankers where moisture is sufficient to keep them alive. With the return of vegetative growth, some sort of fermentation seems to set in and drops of a thick, opaque liquid ooze out of the margins of blight-cankers. These contain countless numbers of the blight bacteria which may swarm into the healthy tissues adjoining, or be carried by any one of the great number of kinds of insects which visit trees at flowering time to the pear-blossoms, to growing tips, or to wounds in tender bark. The pruner with his tools may be an unwilling agent in carrying the bacteria from tree to tree. The organisms now multiply apace, killing tissues wherever they find entrance and causing the several manifestations of the disease described under symptoms. Were it not that the bacteria are killed by sunlight and even brief periods of drying, the life of the plants attacked would be the only limits of the disease unless checked by man. Theoretically, pear-blight can be controlled. Practically, pear-growers fail to control it. Control consists in orchard sanitation whereby the bacterium causing the disease is kept out of the orchard. This proves all but impossible in the average orchard. Sometimes, without doubt, the virulency of the disease is lessened. Possibly, if all the recommendations of plant pathologists could be put in practice, pear-growers would more often succeed in keeping blight down, but the necessary sanitary measures require such watchful care and so great an expense that few pear-growers can carry out the program for controlling this disease. Of those who have studied methods of control and have given advice on the subject, Hesler and Whetzel[24] are as reliable as any and we quote herewith their recommendations: