Plants as Affected by Fungous Parasites. 179 



Sucking insects are not susceptible to poisonous in- 

 secticides, hence we must resort to materials that clog 

 their breathing pores, as kerosene (294), that dissolve 

 their eggs and scales, as potash solutions or that form 

 an air-tight coating over them, as the resin washes 

 (296).* The materials most often used for destroying 

 this type of insects are lime sulfur, kerosene emulsion 

 and tobacco decoctions. 



317. The Life Histories of Injurious Insects, which 

 can not here be taken up, may profitably be studied by 

 the plant grower. A standard work on economic ento- 

 mology will furnish the needed information. 



B — Plants as Affected bt Vegetable Parasites. 



318. Many of the most serious enemies of cultivated 

 plants belong to this class. As a rule, vegetable para- 

 sites contain no chlorophyll, and hence are incapable of 

 forming their own food. While most of them belong 

 to the lower orders of plants, a few species are highly 

 developed and produce true flowers and seeds. 



a — By Flowering or Phanerogamic (phan'-er-o-ga'- 

 mic) Parasites. 



Of these, the only ones sufficiently common or inju- 

 rious to need mention are the broom rape and the 

 dodders. 



319. The Broom Rape of Hemp and Tobaccof is 

 the most injurious species of this class. The seeds ger- 



» The cottony cushion scale, Jcerya purchasi, which was very 

 destructive to the orange In California, has been nearly suppressed 

 by the introduction of an Australian parasite, the YedaUa cardin- 

 aUs. 



t PMlipoea ramona. 



