RUST OF THE ORANGE. 107 



liable to attacks of the Mites, but it is in the intermediate period of its 

 growth that the fruit offers conditions most favorable to their increase. 



Attacks of the Mite always fottawed ~by Rust. The evidence that rust 

 follows as a sequence upon the depredations of this Mite is circumstan- 

 tial rather than direct, but it is also cumulative. Oranges marked and 

 kept under observation, but allowed to remain upon the tree, have in 

 all cases rusted after being overrun by the Mites. Those upon which 

 no Mites made their appearance remained bright to maturity. 



A very large number of observations show a close connection between 

 the occurrence of Mites upon the foliage and rust on the fruit, so that it 

 may be stated as a rule, when the foliage of a tree retains its gloss, the 

 fruit also will be bright, and, conversely, when the condition of the 

 leaves indicates the presence of Mites in great numbers, the fruit will 

 be discolored. 



This is found to be true, not only of the entire tree, but of restricted 

 portions. Thus the upper, the lower branches, or one side of an orange 

 tree may produce rusty fruit while that on the other parts of the tree 

 remains bright. In such cases there will always be a marked difference 

 in the condition of the foliage upon the two portions, and the leaves 

 surrounding the affected fruit will indicate more or less clearly the 

 work of the Mites. 



Other and perhaps more conclusive reasons for considering the Mite 

 responsible for rust will be better understood when the habits of the 

 Mite itself have been considered. 



Interval between the Disappearance of the Mites and the Appearance of 

 liust. As has been already indicated, the Mites do not permanently 

 infest. either the surface of the leaf or the rind of the fruit, but wander 

 off to fresh feeding ground when, through their combined attacks, all 

 the accessible oil-cells have been emptied of their contents, or the tissues 

 have been too much hardened by advancing maturity to be easily pene- 

 trated by their beaks. 



The effects of their punctures upon the cellular structure of the plant, 

 however, continue after their departure, and upon the fruit, rust de : 

 velops with a varying interval, depending possibly upon the relative 

 humidity of the air. Usually the discoloration is very apparent after 

 the lapse of a week, and the rind continues to harden indefinitely, or as 

 long as it is exposed to the air. 



THE RUST-MITE. 



(Typhlodromus oleivorus Ashm.) 



Description. The so-called Bust Insect (Fig. 45, a b) is a four-legged 

 Mite, honey-yellow in color, and about three times as long as broad. 

 The body is cylindrical, widest near the anterior extremity, and tapers 

 behind, terminating in two small lobes, which assist the animal in crawl- 

 ing and enable it to cling firmly to the surface upon which it rests. 

 The front is prolonged in a conical protuberance, which appears to be 



