By Prof. J. C. Arthur.

This is a thesis presented to the faculty of Cornell University on the creation of Professor Arthur to the degree of Doctor of Science. By Pear Blight, Dr. Arthur means what is known as Fire Blight in the Pear - a trouble that has long been a source of serious controversy. Dr. Arthur has been unable to trace its earliest appearance here, though he believes it to be wholly an American disease. Coxe, in 1817, notes it as being at that time a great pest to the pear grower. Dr. Arthur concludes that Prof. Burrill is fully justified in regarding the trouble as directly produced by bacterium, different from that which produces disease in other plants, and which is described and figured here as Micrococcus amylovorus. The paper is reprinted from the "Proceedings of the Academy of.Natural Sciences of Philadelphia".