106 INSECTS AFFECTING THE ORANGE. 



of fungus, but shows the oil-cells to be more or less completely emptied 

 of their contents, and the outer layers, the epithelial cells, clogged with 

 brownish resin, or entirely broken up and divided by fissures, which 

 permit evaporation of the fluids from the underlying cells. The rind of 

 rusted fruit, therefore, shrinks and toughens, and loses by evaporation 

 or oxidation the greater part of its essential oil. 



THE ORIGIN OF RUST. 



Reasons for considering it the Work of a Mite. — If we examine critically 

 with a hand lens of considerable magnifying power the surface of a 

 rusted orange, we will find here and there in the depressions, groups of 

 iniDtite white filaments adhering closely to the rind. Carefully trans- 

 ferring one of these filaments to the stage of a compound microscope, 

 and applying a power of several hundred diameters, the character of 

 the object is clearly shown. It is the cast skin of an insect. 



If the examination chance to be made in winter, when the fruit is 

 ripe, the number of these exuviae will not be strikingly great. But if 

 made in autumn or late summer, the surface of every orange showing 

 rust will be found thickly sprinkled with them, and we shaH be forced 

 to conclude that we have before us the relics of a numerous colony, 

 which at some former period infested the fruit. 



Extending the examination to fruit that as yet shows no indication 

 of rust, we will, if the season is not too far advanced, obtain abundant 

 confirmation of this conclusion, and find these colonies in the full tide 

 of their existence. The former occupants of the cast skins prove to be 

 elongate Mites, of honey-yellow color, too minute to be seen as indi- 

 viduals with the unassisted eye, but visible in the aggregate as a fine 

 golden dust upon the surface of the fruit. 



The Mite on the Leaves. — Having tracked the Mite by means of its tell- 

 tale exuvite, and detected it at work upon the fruit, if we turn our at- 

 tention to the leaves it needs no prolonged search to discover it here 

 also, and in even greater abundance. In fact, it is evidently upon the 

 leaves that the Mites exist and propagate throughout the year; for not 

 onlyare they found upon fruiting trees, but upon plants of all ages, in 

 the nursery as well as in the grove. 



jSTothiug resembling the rust of the fruit follows their attacks upon 

 the leaves. Each puncture of the Mites gives rise to a minute pimple 

 or elevation, until the surface of the leaf becomes finely corrugated, 

 loses its gloss, and assumes a corroded and dusty appearance. 



This tarnished appearance of the foliage is very characteristic, and 

 remains, a permanent indication of their depredations, after the Mites 

 themselves have disappeared. 



First appearance of Mites on the Fruit. — From the time when the 

 cellular strucinre of the rind has completely developed, and the oil-cells 

 have begun to fill, until the fruit is far advanced in the process of 

 ripening; in other words, from early spring until late in autumn, it is 



