88 MANUAL OF GENEEAL AGRICULTURE. 



ively controlled by inspecting the orchard at least once a 

 week during the growing season, beginning as soon as the 

 blossoms begin to fall, cutting out the diseased portions 

 and disinfecting the/ cut surfaces with corrosive sublimate 

 solution made by dissolving one tablet in a pint of water. 

 (See Cornell Bui. 272.) If diseased trees are available see 

 if you can control the disease in this way. 



Question : Point out the practical importance of each 

 of the following facts about Fire Blight : 



1. It is a bacterial disease. 



2. It occurs only in North America. 



3. The bacteria causing the disease pass the winter 

 in hold-over cankers in any of its numerous hosts. 



4. The bacteria get into the host only through 

 wounds. 



5. The chief agents of dissemination are certain in- 

 sects. 



6. The bacteria are usually introduced into the 

 young and growing parts of the host, where in these suc- 

 culent tissues they multiply and develop the disease very 

 rapidly. 



69. THE MOUTH-PARTS OF INSECTS.* 

 Materials: Lens, needle, forceps, grasshopper, honey 

 bee, squash bug, moth. 



Insects that injure plants are of two classes. The 

 distinction between these two classes is in the form of 

 their mouth-parts. One class has its mouth-parts fitted 

 for biting or chewing, while the other 

 class has them fitted for sucking. Meth- 

 ods of destroying insects are based on this 

 difference in the structure of the mouth. 

 Insecticides of one kind are used for kill- 

 ing insects with a mouth fitted for biting. 

 Such insects usually feed upon the leaves 

 of plants. Poisons of different kinds are 

 therefore sprayed or dusted upon the 



leaves. The poison is taken up by the in-p IG 12 . The head 



sect with its food, producing in its ali- of a locust. 

 *From Cornell Rural School Leaflet. 



