INFLUENCE OF TEMPERATURE AND HUMIDITY ON 

 THE GROWTH OF PSEUDOMONAS CITRI AND ITS 

 HOvST PLANTS AND ON INFECTION AND DEVELOP- 

 MENT OF THE DISEASE 1 



By George L. Peltier 



Plant Pathologist, Alabama Agricultural Experiment Station, and Agent, Bureau of 

 Plant Industry, United States Department of Agriculture 



INTRODUCTION 



In the writer's investigations on the susceptibility and resistance of 

 a large number of rutaceous plants to citrus-canker (Pseudomonas citri 

 Hasse) he has been impressed {7-9Y by a number of factors which appear 

 to play an important role in these studies. The factors may be briefly 

 stated as follows : 



1 . The anatomical structure of the plants. 



2. The reaction of the host plants to their environment. 



3. The influence of external conditions on the organism and on 



the susceptibility to infection of the host. 



4. The influence of the host on the virulency of the organism. 3 



THE PROBLEM 



The problem was attacked from the standpoint of the influence of 

 temperature on the growth of the organism and its hosts and on infection 

 and development of the disease and from the standpoint of the influence 

 of humidity on the growth of the organism and its hosts and on infection 

 and development of the disease. 



1 Published with the approval of the Director of the Alabama Agricultural Experiment Station as a 

 report on cooperative investigations between the Department of Plant Pathology, Alabama Agricultural 

 Experiment Station, and the Bureau of Plant Industry, United States Department of Agriculture. 



2 Reference is made by number (italic) to "Literature cited," p. 503-506. 



3 To determine more definitely just what part some of these factors play in governing the susceptibility 

 and resistance of rutaceous plants to canker, leave of four months was granted the writer by the Director 

 of the Alabama Agricultural Experiment Station to carry on this investigation in the Plant Physiology 

 Laboratory at the University of Illinois during the winter of 1918-19. Through the cooperation of Dr. K. F. 

 Kellerman, Associate Chief, Bureau of Plant Industry, United States Department ol Agriculture, a second 

 four months' investigation was made possible the following winter. It is indeed with great pleasure that 

 the writer acknowledges his indebtedness to the University of Illinois for the privileges and facilities of 

 the Plant Physiology Laboratory. The writer is especially indebted to Prof. C F. Hottes for the 

 suggestions, methods, and advice offered during the course of the work and for the time spent by him in 

 preparing, setting up, and regulating the apparatus used. He also wishes to thank Prof. F. L. Stevens 

 for the use of the Plant Pathology Laboratory. The plants used in the experiments were kindly furnished 

 by Mr. W. T. Swingle, in Charge, Office of Crop Physiology and Breeding Investigations, Bureau of Plant 

 Industry, United States Department of Agriculture. 



Journal of Agricultural Research. Vol. XX, No. 6 



Washington, D. C Dec. 15, 1920 



wc Key No. Ala.-7 



(447) 



