118 FLORIDA FRUITS ORANGES. 



or less thinly populated. Deducting, therefore, twenty- 

 seven per cent from the above, we have 50,020 mites, the 

 approximate population of the upper surface. The under 

 side of the leaf was less thickly infested, but the number 

 of mites may be estimated at one half that of the upper 

 face or 25,000. Thus the number of mites and their eggs 

 upon a single leaf is found to reach, even in mid-winter, 

 the enormous sum of 75,000. 



In early summer, when the breeding is active, these esti- 

 mates will be greatly exceeded. At times an orange tree 

 may be so completely infested with the mites that, of its 

 thousands of leaves, very few can be found free from their 

 presence. If, then, we attempt to calculate the number 

 that may exist contemporaneously upon a bearing tree, we 

 find it represented, not by millions but by billions, and 

 the figures obtained convey no definite inpressions to the 

 mind. 



Preference shown for Half Shade. An examination made 

 on a bright, sunny day shows that, while the mites can not 

 long endure the direct light and heat of the sun, they also 

 avoid dark shade. At midday they are more abundant 

 upon the under side of exposed leaves, and although they 

 at all times show a marked preference for light, they de- 

 sert those parts of the leaf or fruit upon which it falls 

 brightest. On a leaf partially exposed to the sun the 

 mites congregate near one edge in the morning, and in the 

 afternoon cross to the opposite side of the same surface, 

 following the shifting shade which, by reason of its curva- 

 ture, the edges of the leaf throw upon one side or the 

 other. 



Rings of Rust on Fruit. On the fruit, this preference of 

 the mites fbr half shade causes a phenomenon which will 

 be recognized as very common on rusty oranges. This is 

 the occurrence of rust in a well-defined ring obliquely en- 



