642 THE POPULAR SCIENCE MONTHLY. 



by placing particles of poison upon the surface of the food-plant. 

 A large proportion of our injurious insects have such biting 

 mouth-parts, but there is also an important class which have, in- 

 stead of jaws, a pointed beak that they push into the cells of the 

 plant and suck out the sap. Insects of this kind can not be de- 

 stroyed by coating the food-plant with particles of poison, because 

 the particles will not be taken into the alimentary system. Con- 

 sequently one must use against them some insecticide which kills 

 by contact. There are several such insecticides in common use, 

 the most important perhaps being an emulsion of kerosene, soap, 

 and water, called the kerosene emulsion. It is usually prepared 

 by adding two parts of kerosene to one part of a solution made 

 by dissolving half a pound of hard soap in a gallon of boiling 

 water, and churning the mixture through a force pump until the 

 whole forms a creamy mass, which will thicken into a jelly-like 

 substance on cooling. The emulsion thus made is diluted before 

 using with nine parts of cold water, and is then sprayed directly 

 upon the offending insects, killing them by simple contact. Among 

 the more important pests against which this insecticide is used, I 

 may mention the aphides or plant lice, the chinch-bug/the various 

 cabbage worms, the lice of domestic animals, etc. 



These examples will perhaps suffice to illustrate how valuable 

 an adjunct the spraying machine has become in preventing the 

 injuries of the hordes of destructive insects that overrun our 

 farms, orchards, and gardens. Turning now to the other class of 

 noxious organisms — the parasitic fungi — we shall find that it plays 

 an equally important role in their subjection. 



As the first illustration under this heading we will take the 

 downy mildew or brown rot of the grape, a disease which for 

 many years has troubled the vineyardists of the Eastern half of 



the United States, and has proved 

 especially destructive in the great 

 fruit belt of northern Ohio, along 

 the southern shore of Lake Erie. It 

 has often destroyed nearly the en- 

 ~1J? ^==^pjsa£^ggp|^pa tj re crop^ ant i several times has 

 _J/ L_ Jll * )\ threatened to ruin the vineyard in- 



dustry over a wide area. Fortu- 

 Fig 5,-Section of Leaf showing nately however, this disaster has 



Mycelium of 1 ungus. Magnified. •> ' ' < 



(After Fallow.) been averted by the timely intro- 



duction of the spraying machine. 

 The brown rot of grapes is a diseased condition of the fruit 

 caused by the presence of a minute parasitic plant — a fungus — 

 that develops by absorbing the tissues of its host. It attacks not 

 only the fruit but also the leaves and young shoots, on which it 

 often appears as a whitish, mildew-like covering, which has given 



