DISEASES OF CULTIVATED PLANTS 529 



and uninjured. The skin on the softened area becomes extremely 

 soft and weak, and is covered first with a white mold, which later 

 produces a blue-green or olive-green powdery layer of spores, giving 

 off a smoky dust when disturbed. There are two closely related 

 fungi, either one of which is able to produce the rot known as blue 

 mold of citrus fruits, and quite often the two species are found to- 

 gether in the same decayed fruit. These two forms may be distin- 

 guished as follows: (1) Penicillium italicum is blue-green in color; 

 and Penicillium digitatum is olive-green as seen after producing 

 spores. (2) Penicillium italicum, produces a patch of blue-green 

 with only a narrow edge of white in the center of a much larger soft- 

 ened area not molded; while Penicillium digitatum produces white 

 surface mold nearly to the extreme edges of the softened area as fast 

 as the decay proceeds, and an olive-green patch begins at the center 

 and enlarges. Since the blue mold follows injuries to fruits, it may 

 be largely prevented by extreme care in picking, handling and 

 packing. 



The wounds through which the blue mold fungus is able to 

 cause decay must be guarded against all along the line, from the time 

 the fruit is being picked until it is loaded into the cars. Clipper cuts, 

 long stems, fingernail scratches, and bruises from pouring into the 

 field boxes, are to be avoided. In hauling, the injuries from splin- 

 ters and rough edges in the boxes, bruises from the bottom of one 

 box being in contact with the top fruit of the box below, and bruises 

 from the jostling of the fruit over a rough road, or in wagons with- 

 out springs, should be avoided. At the packing house, the further 

 injuries that may result from rough handling, as careless emptying 

 of the field crate from too great a height, and sharp corners of the 

 machinery in washing, sizing and packing, are to be constantly 

 guarded against. Poorly constructed washers, sizers and bins in such 

 a position that the fruit is put into too violent motion, are to be 

 avoided. In wrapping and packing, fingernail scratches are to be 

 avoided by wearing gloves. (See Mechanical Injuries.) Not only 

 must the slight injuries to the fruit be guarded against at every turn, 

 but the field boxes, wagons, packing houses, and all machinery 

 should be kept clean and free from contamination with blue mold 

 spores from rotted fruits lying about. Packing houses in which culls 

 or other inferior and worthless fruit are permitted to remain for even 

 a part of a day, are pretty certain to become badly contaminated 

 with blue mold spores. These invisible spores are carried to all parts 

 of the structure by means of the ordinary air currents. Groves in 

 which drops are allowed to remain also become permeated with these 

 spores. Under the conditions which ordinarily prevail, it is almost 

 literally true to say that blue mold spores occur everywhere. 



Stem-End Rot. Like anthracnose this disease makes its pres- 

 ence evident by an unusual amount of dropping. This rot begins in 

 a circular patch about the stem end. At first the circular area is light 

 brown or very little discolored on mature fruit, but dark brown to 

 leather colored on immature fruit on the tree. The rind remains 



