428 DISEASES OF THE APPLE. 



side ; this terminates with a button, or knob-like 

 end. The larvae are maggots without feet, and 

 with the breathing-holes generally in the hinder 

 extremity of the body. The pupae are mostly in- 

 cased in the dried skins of the larvae ; sometimes, 

 however, they are naked, in which case the wings 

 and the legs are visible, and are more or less free 

 or un con fined. 



7. Hijmenoptera. These insects have a perfect 

 change of form. Their mouth is armed with dis- 

 tinct mandibles, or jaws, and also has a ligula, 

 tongue, or proboscis for suction. They have four 

 membraneous wings, divided into large cells. The 

 larvae are mostly maggot-like, or slug-like; that 

 of some species are caterpillar-like pupae, with legs 

 and wings unconfined. 



h II. DISEASES OF THE APPLE. 



I. Those affecting the Leaf. 1. The fall of 

 the lecf — Phijlloptosis. In most plants there is a 

 point of articulation between the leaf-stock and the 

 wood, but not always. Nearly all the plants which 

 come under our notice in this work possess such a 

 junction. When the leaf is about to fall, a chemical 

 change takes place in the chlorophyl, which gives 

 the green color to plants, — a change by which they 

 assume the hue so familiar to us as that of autumn. 

 Thus the leaf dies, and is no longer of any value to 

 the tree. 



