Apr. lo. 1916 Citrus Canker 97 



lesions. The primary cause of the disease is Pseudomonas citri, first 

 isolated by Hasse from grapefruit and found to be pathogenic on 

 grapefruit seedlings. This has been confirmed, and in addition an 

 organism presenting the same cultural and physiological characters has 

 been isolated from trifoliate and Satsuma oranges and lemons. No 

 difficulty has been experienced in cross-inoculating the organism on 

 McCarty and seedUng grapefruit, Pineapple oranges, Satsuma oranges, 

 and seedling trifoliate oranges. It grows readily on a variety of artificial 

 media, and according to the studies made its group number is 221.3332513. 



Infection occurs through natural openings and through wounds. The 

 rapid spread of the disease is favored by the simultaneous occurrence of 

 newly exposed cankerous cells and the presence of a film of moisture, 

 especially on young parts of the plant. The bacteria occur for the most 

 part between the cells of the host and cause them to become considerably 

 hypertrophied. Little, if any, hyperplasia is believed to occur. This 

 enlargement of the cells is caused by the dissolution of the middle 

 lamellae through enzym activity and by a modification of the host 

 protoplast so that its osmotic pressure is increased. This increased 

 pressure results from the presence of the parasite between the cells and 

 from the passage of materials through the walls of the host, occasioned 

 by the growth of the organism. 



Besides Pseudomonas citri, fungi belonging to the genera Phoma, 

 Fusarium, and Gloeosporium have been isolated from Citrus cankers. Of 

 the fungi Phoma sp. alone was found to be notably active in the disin- 

 tegration of the tissues. It is able by virtue of the secretion of specific 

 enzyms to utiUze the carbohydrates, cellulose, starch, maltose, and 

 saccharose and causes also a decrease in acidity of invaded tissues. It is 

 regarded as heretofore undescribed and is herein given the name " Phomxi 

 soda, n. sp." 



The difference in susceptibility to Citrus canker of Satsuma oranges 

 and grapefruit can not be accounted for on the basis of differences in 

 total organic acids in the two hosts. 



Comparative analyses of grapefruit leaves aJEFected with Citrus canker 

 and of healthy leaves shows that there has been in diseased leaves a de- 

 crease in all of the soluble and insoluble carbohydrates due to their 

 utilization by means of sucroclastic enzyms secreted by the canker 

 organisms. Apparently a decomposition of the host proteins occurs 

 concurrently with their synthesis in the metabolism of the parasite pro- 

 teins, and there results a slight increase in total nitrogen in diseased 

 tissues. The slight increase in phosphorus in diseased tissues is ac- 

 counted for in the same manner as that in nitrogen, since they appear to 

 be correlated. No differences in ash were found in fraction 3, and the dry 

 weight of diseased tissues was slightly greater than that of normal. 



Rain and dew are important agencies in the dissemination of Citrus 

 canker. Any other agencies, of which man is probably the most im- 



