DISSOLVING enzyme; s. 87 



Pectase is especially abundant in growing tissues, and is supposed to play an important part in 

 this lamella formation by converting the pectose of the inner lamellse into the more soluble pectine 

 and ultimately into pectic acid, which then passes to the outer surface of the inner lamellae where 

 it combines with calcium and increases the middle lamella substance. The latter appears homo- 

 geneous, but is distinctly stratified in structure, at least at the angles of the cells. 



Jones gives the following description of the appearance of attacked tissues : 



" B. carotovorus rots only parenchymatous tissues. The invaded tissues become watery and 

 usually more or less darkened in color when exposed to the air. The attacked cells rapidly lose all 

 coherence and always show a sharply defined line of demarkation, indicating that the softening 

 occurs quickly and completely after it begins. Examination of such recently decomposed tissues 

 under the microscope shows the cells to be already isolated or easily separable along the plane of 

 the middle lamella. The protoplasmic sac within the cell is collapsed, more coarsely granulated 

 than normally, and evidently dead and in the process of disorganization. Bacteria teem around 

 and between these cells but are so rarely seen within them that where this does occasionally occur, 

 one is led to attribute it to mechanical rupture of the softened walls rather than to direct solution." 



If a cut surface of root is inoculated and kept in an ordinarily dry atmosphere, the infected area 

 dries out very rapidly, but if, on the other hand, it is kept in a saturated atmosphere drops of exudate 

 teeming with bacteria form on the surface and the tissues underneath become sunken. Wilting 

 or pithy and partially dried-out vegetable tissues of even the most susceptible varieties, such as 

 turnip, radish, and carrot can not be infected by this organism. The areas actively invaded are the 

 intercellular spaces and the planes of the middle lamellae. An abundant moisture content in the 

 host tissues is necessary for this invasion. The expulsion of gas caused by the filling of the inter- 

 cellular spaces with liquid resulting from the plasmolysis of the cells, and the changes in the optical 

 character of the walls themselves probably accounts for the water-soaked appearance of the invaded 

 tissues. The walls are normally uniformly refractive throughout, but the inner lamella begins 

 to lose its refractiveness almost immediately when it is immersed in a living culture of B. caroto- 

 vorus or an aqueous solution of the precipitated enzym. This change is evident to the naked eye 

 if thin sections are used, and microscopical examination shows that it is associated with a swelling 

 of the inner lamellae, sometimes to twice their original thickness, this phenomenon being followed 

 within a short time by a delicate laminated appearance of these swollen walls. The middle lamella 

 also becomes less refractive, and the thinner portions soon begin to melt away. As these parts of the 

 middle lamella dissolve, the heavier portions in the angles of the cells remain isolated. When this 

 stage is reached, tapping on the cover glass will show that the cells have lost all cohesion. It requires 

 from ten minutes to an hour for thin razor sections of carrot or turnip placed in living cultures or 

 in active enzym solutions to pass through these changes, although the complete solution of the thickest 

 pieces of intercellular substance may not have taken place in this time. There is also a slight thinning 

 of the inner lamellae, but complete solution has never been observed, although the same sections have 

 been under observation for three weeks. There was little change after the first few hours. The 

 cellulose reaction is obtained even after the longest immersion. The lamination of the walls grows 

 more apparent for a short time, but no further change takes place. 



There is no action upon lignified or cuticularized walls. The solution of the middle lamella 

 takes place considerably in advance of the invasion of the organism. 



In the invasion of turnip and radish roots and cabbage petioles the conditions are similar to 

 those found in the carrot but the rotting advances more rapidly. In the carrot the core rotted more 

 quickly than the cortex tissues. The young potato became disintegrated more quickly than the 

 mature tuber. On the beet root there was no solvent action whatever. 



These studies indicate that aside from the moisture content, susceptibility to infection is largely , 

 if not wholly, dependent on the nature of the middle lamella. 



Comparative studies were made with 45 other strains of soft-rot organisms, including the 

 following : Three strains of cabbage-rot bacill i isolated in Vermont by F. R. Pember in 1 899 ; twenty- 

 three other strains of cabbage-rot bacilli isolated in Vermont by W. J. Morse in 1901; one strain 

 of turnip-rot bacillus isolated by 1,. P. Sprague in Vermont, 1903; twelve strains of soft-rot bacilli 

 isolated by Harding and Stewart in New York, including one associated with the soft rot of Amor- 

 phophallus simlense, and eleven from the soft rot of cabbage; six additional organisms, as follows: 

 Townsend's calla rot, Bacillus aroideae; Harrison's cauliflower rot, Bacillus oleraceae; van Hall's 

 two iris-rot organisms, Bacillus omnivorus and Pseudomonas iridis; Spieckermann's kale-rot organism 

 (a Bacillus) ; and Potter's turnip-rot organism, of which the strain sent by Potter to Jones was also 

 a Bacillus. 



