324 GENERAL SCIENCE 



so are the moulds that grow upon foodstuffs, and the rusts 

 and mildews that are so destructive of grain crops. They 

 are parasites (see page 40), and are the cause of losses in 

 agriculture estimated at hundreds of millions of dollars 

 annually. 



Bacteria form a class of plants closely related to the fungi. 

 In man's struggle for existence the microscope has made 

 possible a knowledge of these hidden agencies which have so 

 long worked havoc with his food supply, with his health, 

 and with life itself. In the field of agriculture science has 

 scored some of its greatest triumphs. Intelligent as well as 

 persistent efforts are necessary in order to be assured of 

 success in a never ending warfare against insects and plant 

 diseases. It must not be forgotten that in this warfare the 

 birds are man's friends, and an active agency in the destruc- 

 tion of insects. 



SUMMARY 



It is an easy matter to buy and set out apple trees, and to get them 

 to grow till large enough to bear. But there is occasion to wonder why 

 the apples growing upon them are so poor oftentimes, and the trees 

 so" short lived. It is only by persistent efforts that the destruction 

 wrought by the codling moth can be combated successfully. Various 

 fungus growths sap the strength of the trees, and finally kill them. 



To spray successfully trees with large tops, using the poisonous com- 

 pounds either as a liquid or as dust, requires a powerful force pump, 

 or a compressed air outfit. To move the equipment and the materials 

 used from tree to tree through an orchard, and to furnish the necessary 

 labor for several applications every season, involves much expense. 

 But it is only by spraying that the trees and their fruit can be saved. 



The fungi are a class of plants wholly destitute of chlorophyll, and 

 therefore utterly unable to prepare food for themselves from the raw 

 materials of sap water from the ground and carbon dioxide from the 

 air. As parasites the fungi thrive by living upon the food prepared by 

 other plants that do have chlorophyll, thus robbing those other plants 

 and possibly in time starving them to death. The annual losses in 

 the agricultural productions of this country -from fungus growths on 



