384 Journal of Agricultural Research voI.v.no.q 



The killing of the host cells, so far as is revealed by the microscopical 

 examination, seems due principally to a modification of the osmotic 

 relations of the cells as a result of the disappearance of the middle lamella 

 and to much of the liquid contents of the cells being withdrawn by the 

 fungus to be used in its development. In the plum the chloroplasts and 

 chromoplasts contained in the cells lying directly under the epidermis 

 appeared not to be disintegrating in those cells which had not so col- 

 lapsed as to make observation impossible. The cytoplasm of the deeper- 

 lying cells was very scant, but showed evidences of plasmolysis, often un- 

 mistakably in advance of the penetration of the hyphae (PI. XXXIX, fig. 3). 



MIDDLE-LAMELLA SOLVENT 



The nature of the substance secreted is not at all clear. From the 

 effect on the host tissue it would appear that the middle-lamella-dissolving 

 enzym pectinase was produced, but attempts to isolate it were without 

 success. 



Juice was pressed from rotten portions of apples and loquats {Eriohotrya 

 japonica) infected with the brown -rot fungus. This was filtered imder 

 sterile conditions, in some cases through coarse, and in others fine filter 

 paper. Slices of healthy apple and loquat fruits were partially immersed 

 in the liquid, but showed no softening effect in any case after several 

 days. Further trials with a method to be described later, used in sepa- 

 rating pectinase from Penicillium expansum, also gave negative results 

 with 5. cinerea. 



In another case a partially rotted apple plug was put into a test tube on 

 cotton above commercial formalin so that the plug did not come in con- 

 tact with the liquid. It was thought that the fungus would be killed by 

 the fumes, but that if a pectinase were present it would continue to rot 

 the tissue. No further rotting took place, and at the end of five days the 

 tissue, unaffected at the beginning, was still firm and of normal color. 



An attempt was made to isolate the enzym pectinase from a culture of 

 S. cinerea, 86 days old, on apple cider. The method used was that de- 

 scribed by Pringsheim (1910), which consists, in brief, of thorough drying 

 of the material with acetone, followed by pulverization of the dried 

 material and extraction of the enzym with a small quantity of water. 

 On May 8, 1915, succulent twags of BXW21 plum, sand cherry, and pear 

 (Pyrus heiulifolia) were partially immersed in the liquid extract in test 

 tubes; also pieces of ripe apple the flesh of which was sUghtly mealy, and 

 pieces of young peaches, one-quarter grown, were entirely immersed. 

 The tubes were placed in a constant-temperature oven at 35° C. Checks 

 were rim, using water in place of the extract. 



After 24 and 48 hours the plum, pear, and sand-cherry twigs showed 

 no effects from the treatment other than a sUght wilting. The tissues 

 were not softened. The blocks of green-peach fruit showed no softening. 

 After 15 hours the apple pmg had softened slightly over the surface, but 



