by piercing- the outer tissues of the plant and sucking- up the juice, called 

 insects with sucking mouth parts. The first group of insects, among 

 which we find grasshoppers, cucumber beetles, codling moth larvae, cur- 

 rant worm, and a great many others, can be poisoned by covering the 

 surface of the plant upon which they feed with some poisonous material ; 

 while the second group, since they do not eat the surface of the plant but 

 feed only on the inside juices, must be destroyed by means of some sub- 

 stance which will act upon their bodies, as caustic washes, or something 

 which will act upon their breathing pores, smothering them, such as a 

 gas. 



This, then, divides insecticides into two groups : food poisons and 

 contact insecticides. 



There are some insects, however, owing to their peculiar habits, in- 

 accessibility, or other causes, which require special treatment, such as 

 the cut worms, which work underground, and the grain weevils, which 

 affect stored products ; the ones which feed inside the bark or within the 

 stem of the tree or plant, such as the apple tree borer or the raspberry 

 cane borer ; the household pests ; and the animal parasites. 



Classes of Fungi. 



A fungus is a plant which feeds upon other plants, and is thus a para- 

 site. It begins with a seed (spore) which germinates and produces a 

 great number of small thread-like structures which correspond to the 

 roots, stem, and leaves of an ordinary plant, and called the mycelium. 

 Sometimes this mycelium develops wholly upon the surface of the plant 

 or fruit, as with the powdery mildew of the grape ; while at other times 

 the germ tube of the spore penetrates the skin and produces its mycelium 

 within the tissues, just as happens in the case of the grain rusts and 

 smuts, downy mildew, and a great many others. 



Fungi, then, can be classed as external and internal, and the method 

 of dealing with them varies accordingly. Those of the first kind can be 

 attacked and destroyed by use of proper materials, but the second kind 

 can only be prevented. 



INSECTICIDES. 

 Food Poisons 



Food poisons are that class of compounds which contain some 

 poisonous substance that if eaten and absorbed by the system will cause 

 death. The most commonly used material that produces this toxic effect 

 is arsenic, but other materials may be and are used. 



"White Arsenic," known also as arsenious acid, arsenious oxide, 

 A? 5 3 -, is the basis of practically all food poisons. It is a white powder, 



