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INSECTICIDES AND FUNGICIDES 



215. Fungi. — Fungi are plants which have no chlorophyl 

 and are consequently dependent on host plants for all their 

 food. They are propagated by spores which are produced 

 in great numbers and can be easily disseminated. When 

 the spores germinate on some suitable host, a little tube is 

 put forth, from which develops the mycelium. Some fungi 

 grow mostly under the surface, the spore tube entering by 



Fig. 70. — Spraying an orchard. Department of Experimental Pomology, 



Pennsylvania Station. 



the stomata or other openings in the leaf or stem. These are 

 fungi like the brown rot and grain smuts. Other fungi grow 

 on the surface, like the powdery mildew. Internal fungi 

 cannot be killed after they have gained entrance to the 

 host, but must be caught before the spore germinates, by 

 covering the plant with a poison which kills the spore or 

 germ tube. External fungi can be killed at any time because 

 they are always exposed. 



