FUNGOUS AND PHYSIOLOGICAL DISEASES. 



475 



Treatment. The disease can be held in check by spray- 



ing with Bordeaux mix- 

 ture or ammoniacal solu- 

 tion. 



Ripe-rot of Citrus 

 Fruits. Frequently ripe 

 specimens of citrus 

 fruits, more particular- 

 ly, perhaps, oranges and 

 lemons, show a yellow 

 covering of dust- like, 

 bluish powder. If ob- 

 served in an earlier 

 stage, the area will be 

 whitish, instead of blu- 

 ish, later the whole fruit 

 ball becomes small and 

 shriveled and the powd- 



^J Substance OCCUpiCS a 

 relatively larger SpaCC. 



The rotting of the fruit is caused by a fungus, Pemcil- 

 lium lialicum, closely allied to the common blue mold 

 which forms on bread, and the powdery mass is composed 

 of innumerable spores. The white coating of the fruit, on 

 some injured spot, is the "mycelium'' the vegetative part, 

 which bears the same relation to the fungus that the roots 

 do to a higher plant. The mycelium grows into 

 and through the tissue of the fruit. After de 

 veloping for some time and reaching a certain 

 stage of growth, the fungus forms spores. These are vis- 

 ible as the bluish, powdery moss. The spores are joined 

 together in the early stages in bead-like strings. As they 

 become matured, they break off and blow away. They are 



Pig. 102. Leaf-spot fungus on pomelo leaves. 

 The light areas are the spots affected. 



