Apr. lo, 1916 



Citrus Canker 



83 



of nutritive substances through the cell walls must exert an influence 

 on the concentration of the cell sap. Then, too, the gelatinous material 

 making up the bacterial cell walls certainly possesses considerable 

 power of imbibition. 



Further it has previously been pointed out that Pseudomonas citri 

 exerts a strong diastatic activity when grown on potato cylinders. The 

 production of this enzym has also been demonstrated by growth on 

 starch agar prepared according to the method described by Crabill and 

 Reed (4). Within a week a clear halo around the edge of the bacterial 

 colony is formed on this substratum, thus making a striking ocular 

 demonstration of dissolution of starch by the canker organism. If 

 diastase, secreted by this organism, is readily diffusible through the cell 

 walls, and it is reasonable to suppose that it is, it can convert the rela- 

 tively insoluble starch into more soluble carbohydrates and thus increase 

 the osmotic pressure of the cell sap. 



It is not impossible that these several causes of increased osmotic 

 pressure operating conjointly or separately may so profoundly modify the 

 imbibitory properties of certain col- 

 loidal substances within the cells that 

 their affinity for water is in conse- 

 quence greatly increased. 



No attempt has been made to de- 

 termine the isotonic coefficient of the 

 cell contents of the enlarged cells, but 

 for the reasons just mentioned it is 

 believed to be greater than that of 

 normal cells. 



DISINTEGRATION OF THE TISSUES 



Fig. 7. — Cross section in outline of a spongy canker 

 on the rind of a fruit of Citrus decumana, show- 

 ing ruptured epidermis and hypertrophy of the 

 rind tissues, the cells of which are loosely at- 

 tached. 



An attempt has been made to gain 

 certain information relative to the 

 organisms involved in the disintegra- 

 tion of cankerous tissues, together with the nature of their activity on this 

 tissue. It was previously pointed out that a species of Phoma is com- 

 monly associated with Citrus canker. Two other species of fungi belong- 

 ing to the genera Gloeosporium and Fusarium are also sometimes 

 present. Since certain bacteria and fungi are known to possess the power 

 of hydrolyzing cellulose (13, 15), of which complex substance cell walls 

 are largely constituted, an effort has been made to study the action of 

 the organisms associated with canker upon pure cellulose. For this 

 purpose cellulose agar was prepared according to the following method. 

 Schweitzer's reagent was first made by adding ammonium chlorid and 

 then an excess of sodium hydrate to a solution of copper sulphate. The 

 blue precipitate thus formed was washed, pressed on a cloth filter, and 

 dissolved in ammonium hydrate (sp. gr. 0.92). In this solvent 15 gm. 



