RUST ON THE ORANGE. 137 



to active circulation of sap, the pressure from within 

 induces a more active flow of oil. Hence the rain 

 makes the show of rust the more speedy by first 

 stimulating to an increased flow of oil and then 

 hastening its oxidizing. The rust does not appear 

 simultaneously with the insect, but follows its opera- 

 tions. Hot weather is favorable to the development 

 of the insect, but wet weather increases the show 

 of rust. 



