APPLE DISEASES 93 



sort on the surface of an apple, it germinates and its mycelium 

 proceeds to feed on the ripe fruit. Among the common types of 

 wounds through which P. expansum gains entrance may be 

 noted, finger-nail cuts, bruises, worm-holes, scab spots, and 

 spray-injured places. The fact that the soft-rot fungus gains 

 entrance to the apple through such injuries is highly important 

 in the matter of controlling the disease. It is further worthy 

 of attention in this connection that this pathogene cannot 

 enter normal, unbroken skin. Accordingly it will be learned on 

 observation that in barreled apples of a good quality those fruits 

 at the heads of the barrel are rotted more extensively than 

 those in the center of the barrel. 



Like many fungi, P. expansum develops an extensive system 

 of mycelium in the lesion. From the germ tube, hyphse grow 

 in all directions into the flesh. The threads dissolve their way 

 between the cells of the fruit-pulp, as a result of which the latter 

 are easily pushed out of position. They slip over each other at 

 the slightest pressure. Thus when the surface of a rotted area 

 is pressed by the finger the tissue quickly and easily gives 

 way, offering no resistance whatever. The disease is well 

 named soft-rot. As already mentioned, under conditions of 

 high relative humidity greenish cushions or pustules appear 

 on the surface of the affected area. These are tufts of fruiting 

 stalks of the fungus which arise from the mycelium within. 

 Numerous hyphse grow in erect fashion at the same point ; 

 their general arrangement is not unlike that of an inverted 

 broom without the handle. The tips of these hyphse, or 

 conidiophores, become branched in a digitate fashion, and at 

 the end of each stalk is developed a chain of spores, or conidia. 

 The number of conidia which might be produced on the surface 

 of a single rotten apple would aggregate millions. As soon as 

 mature these spores are easily broken from the conidiophore 

 and, being extremely light in weight, float about in the air for 

 some time. 



