THE PROPAGATION OF PLANTS 127 



oats germinate in the soil the following spring, the spores 

 germinate also and send slender, thread-like organs up- 

 ward in the tissue of the oat stem as it develops. Thus 

 we actually have one plant growing at the expense of and 

 within the tissues of another. About the time the oat 

 begins to flower, these thread-like organs push their way 

 into the base of the flower. Here they take the nourish- 

 ment which was intended for the seed (Section 92 and 

 Exercise 24), prevent its development and develop 

 instead a mass of loose, black spores. The loss to farmers 

 of the United States in a single year, caused by this smut 

 plant, has been over twenty million dollars. We shall 

 consider shortly how to prevent the spread of this disease. 



97. How Spores are spread. — As agricultural students, 

 we are not particularly interested in the spores of plants 

 like the fern and the moss, but the manner in which the 

 spores of the disease-producing plants are spread is of 

 vital interest to us. The different ways by which spores 

 may be spread, or disseminated, may be grouped as 

 follows : 



First : on seeds, which are carried from place to place. 

 Oat smut, stinking smut of wheat, potato blight, anthrac- 

 nose of beans, and many other diseases are spread in this 

 way. 



Second : in the soil. The spores of the root rot of cotton, 

 potato scab, root rot of the beet, and many others live 

 through the winter and spread more or less through the 

 soil. 



Third : on dead leaves, stems, roots, weeds and grass. 

 Many spores of the disease-producing plants pass their 

 winter stages on this kind of material. When the warm 

 weather of spring comes on, the spores develop, spread 

 and attack growing plants. 



Fourth : by diseased and fallen fruit. The old, withered 

 plums, which hang on the trees all winter, harbor the 



