CHAPTER VIII. 

 BUST OF THE ORANGE. 



NATURE OF RUST. 



Discoloration of the Fruit The brownish discoloration of the rind 

 of oranges, familiarly known under the name of "rust," has, since the 

 production of this fruit became an important industry in Florida, given 

 great concern to the producers, and occasions annually serious loss by 

 affecting injuriously the salableuess of the fruit. In appearance the 

 rust varies from a light or dark brown stain beneath the cuticle to a 

 rough incrustation resembling an exudation of resinous gum upon the 

 surface. In the former case the golden color of the ripe orange is more 

 or less obscured, and in the latter entirely destroyed by the discol- 

 oration. When entirely coated with rust the surface becomes finely 

 chapped and roughened, giving to the unripe fruit a likeness to russet 

 apples. 



The season during which rust makes its appearance includes nearly 

 the entire period of growth of the fruit, beginning in early summer, 

 when the fruit has attained less than one-third its full size, and contin- 

 uing late into autumn. Its most rapid increase is, however, in August 

 and September, as the orange approaches maturity. Rarely is there 

 any real increase after the rind begins to ripen, although the discolor- 

 ation usually attracts attention just at this time, and frequently occa- 

 sions unnecessary alarm. On the contrary, there is always a percep 

 tible brightening as the fruit attains its full color, and oranges slightly 

 affected, or affected very early in the season, when fully ripe show but 

 little trace of rust. 



J* Rust a Fungus, or an exudation of Gum? The term "rust" is very 

 indefinitely applied to a great variety of plant diseases, some of which 

 are clearly due to the presence of fungi, and others are considered path- 

 ological conditions of the plant, attributable to, for the most part, un- 

 known or conjectural conditions of soil or climate. 



A good example of the first class is found in the common and very 

 destructive rust of the Fig. Any one who will take the trouble to ex- 

 amine with a good glass the brown discoloration upon the surface of 

 the leaves may easily detect the sacks, or asci, of the fungus, filled to 

 bursting with the spores, or pouring them out upon the surface. 



Nothing of this kind is seen upon the leaves or rusted fruit of the 

 Orange. A microscopic examination of the fruit-rind reveals no forms 



lOt 



