[Chap. XLV PLANT DISEASES 581 



When fox-fire is traced to its source it is usually found coming from 

 saprophytic fungi (Fig. 263) living in partially decayed wood or bark. 

 Some of the energy set free in respiration in these fungi is light energy. 



The smuts. The smuts described in the preceding chapter are de- 

 structive to cereals, but effective measures of controlling some species 

 have been discovered. The importance of knowing exact life histories 

 of fungi that cause disease before one attempts to formulate methods of 



Fig. 263. Fox-fire. Fungous mycelium in a piece of wet bark as seen in light and 

 in darkness. After W. Hamilton Gibson. 



control is shown by a study of three kinds of smuts: corn smut, loose 

 smut of oats, and loose smut of wheat and barley ( see Chapter XLIV ) . 



The spores from the black masses or lesions on the corn plant fall on 

 the ground, remain there over the winter, and may be the source of 

 infection of young plants if carried to wounds during the following 

 spring. The most effective methods of control are selection of seed 

 from healthy plants, selection of hybrids immune to the disease, and 

 crop rotation. 



The mycelium of the fungus which causes the disease known as loose 

 smut of oats grows within the oat plant and produces millions of spores 

 in the young flower panicle. These spores are blown about by the wind 

 and some of them lodge in the flowers of healthy oat plants. There 

 they germinate; and the mycelium may grow among the glumes, or 

 beneath the epidermis of the grain coat. Some spores may not germinate 

 but remain attached to the outer portion of the glumes. The fungus 

 overwinters in either of these three places, and when the oats are sowed 

 may cause infection of the seedling and eventually a smutted head at or 

 before harvest time. The fungus is killed by treating the seed with 

 formaldehyde or with ethyl mercury phosphate before planting. 



The fungi causing loose smut of wheat and barley live through the 



