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called aerial hyphae, spring from threads or roots of the 

 fungus within the leaf, and are called, collectively, 

 mycelium, also known as submerged hyphae. The 

 fungus lives within the plant, feeds on its juices, 

 ultimately breaking up its structure, causing the plant 



Fig. 14 A potato-leaf, showing the spots and patches of " potato- 

 disease," due to the ravages of Phytophtlwra infestans. In the darker 

 patches the tissues are quite dead : the margins of the spots would 

 show the hyphse of the fungus, standing off much as in Fig. 15. After 

 Sorauer. 



to die. It is a parasite of the potato, much in the same 

 way that the mistletoe is a parasite of the oak or apple- 

 tree. 



Perhaps the parts of the fungus can be best under- 

 stood if they are compared with the parts of a plant of 

 wheat. First, the roots of the fungus running within 



