198 THE PRINCIPLES OF FLORICULTURE 



fungus becomes established in the plant's system. Oc- 

 casionally, the fungus is a secondary agent in destroy- 

 ing plant tissue. Insect attacks may be the primary 

 cause, and the fungus gains entrance to the vital part 

 of the plant through injuries caused by these agents. 

 Various forms of plant diseases often follow attacks of 

 aphis. These insects penetrate the epidermal tissue and 

 expose the delicate substratum. Injuries also occur to 

 plant tissue through mechanical means or in handling 

 the plants, and as a result, disease may occur. It is a 

 well-known fact that when a limb is cut from a tree, the 

 spores of various wood-destroying fungi gain entrance 

 to the tissue of the tree, through the exposed surface. 

 Unless some antiseptic material is used to prevent ger- 

 mination of the spores, their development and growth 

 are very rapid. When the epidermal formation is nor- 

 mal, fungi less frequently gain an entrance to the plant. 

 167. Methods of combating parasitic fungi. The 

 following methods are suggested by Tubeuf : 1 



"A. Methods for extermination and removal of parasitic fungi 

 alone. 



(1) Killing of fungi attached to seed, through sterilization 



by means of hot water or copper steep mixtures. 



(2) Combating leaf-frequenting fungi by dusting or spray- 



ing with mixtures containing sulphur or copper. 



(3) Excision and extermination of the sporophores of Poly- 



porese and Agarcinese on orchard or garden trees. 



(4) Removal and destruction of dead parts of plants carry- 



ing sporocarps or other hibernating stages of any 

 fungus. 



B. Methods for combating fungi by removal of diseased plants 

 or plant organs. 



(1) Removal of the parts of a host plant harboring fungi. 



(2) Removal of the whole or part of a complementary host 



l " Diseases of Plants Induced by Cryptogamic Parasites," 

 Tubeuf and Smith. 



