174 Principles of Plant Culture. 



as extension rods, are most frequently made of a bamboo 

 pole through the center of which has been run a small 

 brass tube. 



Nozzles are of various types, but one which breaks 

 the spray up into a fine mist is, as a rule, most desir- 

 able. The cyclone or eddy-chamber type of nozzle, of 

 which the Vermorel is a good example, seems to be 

 most efficient in producing this character of spray and 

 is consequently most largely used. The Bordeaux type 

 of nozzle is used to some extent for special purposes. 



Many of the common spray materials are merely held 

 in suspension in the water with which they are diluted 

 and unless there is some means of keeping the water 

 in motion they settle to the bottom of the container, 

 making even distribution and efficient work impossible. 

 Spray pumps should therefore be fitted with an agi- 

 tator to keep the spray materials in suspension. 



305. The Use of Insecticides. In treating any given 

 insect, the most important question to decide, is the 

 manner in which it appropriates its food, as upon this 

 will depend the preventive measures to be used. 



306. Injurious Insects are referable to Two Classes, 

 viz., eating insects, i. e., those feeding directly upon the 

 plant tissues, such as the potato beetle, the apple-tree 

 borers,* the plum curcolio,t and the sucking insects, i. e., 

 those feeding only upon the juices of the plant, such as 

 plant lice, the squash-bug,t and the oyster-shell scale. § 



307. The Eating Insects may be subdivided into leaf- 

 eaters, those that devour the foliage; root-eaters, those 

 that devour the roots; and burrowers, those that har- 



* The round-headed &pple-tree borer, Saperda Candida; the flat- 

 headed apple-tree borer, Chrysotothria femorata. 



t Conotrachelus nenuphar, t Anasa tHstis. § Lepidosaphes ulmi. 



