THE FUNGI 281 



FUNGI AND PLANT DISEASE 



Nature and importance. The diseases of plants caused by 

 fungi are scarcely less important than the diseases of animals 

 and man, on account of their intimate relation to the world's 

 food and lumber supply. These facts were abundantly empha- 

 sized to the public during the Great War, when government 

 and state experts demonstrated the immense importance of 

 fungous pests to our national food supply. We have only to 

 recall the damage done by such fungi as the grain rusts and 

 smuts, the potato rot, the apple scab, the grape mildews, and 

 the tree-killing fungi to realize the national importance of fungi 

 and fungous diseases. 



Some plant diseases are produced by bacteria, as in man and 

 animals, but the greater number are caused by filamentary fungi 

 similar to the molds, rusts, and smuts studied in previous pages. 



Spread of plant diseases. The rapid spread of plant diseases 

 is due in large measure to the very unusual number of asexual 

 spores produced by the fungi, of which we have had illustrations 

 in the molds, smuts, and mushrooms. Indeed, many fungi, like 

 the mushrooms and smuts, have apparently abandoned the sexual 

 method of reproduction entirely for the more rapid method of 

 producing abundant asexual spores. 



These spores are light and so, like the bacteria, are constantly 

 blown about and carried long distances by air currents. As a 

 consequence some fungous diseases spread with startling rapidity, 

 resulting in widespread injury. 



The recent spread of the disease known as chestnut blight, 

 caused by the fungus Endothia parasitica, is a well-known illus- 

 tration of the rapid spread of such a destructive disease by means 

 of spores. The chestnut blight is supposed to have been imported 

 from China and to have spread from New York City, as a center, 

 about 1904. It has now almost wholly destroyed the native chest- 

 nut trees over large areas in the forests and cities of the eastern 

 United States. The pine-tree blister rust has had a similar his- 

 tory and threatens to destroy many thousand feet of valuable 

 pine timber unless its ravages can be checked. 



