THE LOOSE SMUT 



189 



■until it is nearly time for the oats to blossom. Then 

 comes a sudden change; the spores develop rapidly, and 

 are dry, powdery masses before the plants are through 

 blooming. When one of the branches of a stooling 

 plant is infested, the others from the same root usually 

 are also, a result of the entrance of the smut so soon 

 after the seed germinates. It sometimes happens that 

 only a part of the spikelets of a head are attacked, and, 

 according to Kellerman and Swingle, 'Mn a few cases 

 smutted heads have been collected where the smut has 

 destroyed the grain and flowering glumes, while the 

 large outer husks are yet entirely sound. Such a head 

 would scarcely be seen to be smutted unless carefully 

 examined." Most of the best authorities agree that 

 there is very little danger of infecting oats with smut 

 from the spores in barnyard manure applied to the soil. 



The mycelium of the oat smut fungus is composed 

 of extremely delicate threads, aud the spores are very 

 minute, ranging from one-five thousandth to one-three 

 thousandth of an inch in diameter. 'They are oval, or 

 sub-globose in shape, with the outside wall spiny, or 

 warty, having minute elevations all over its surface. 

 One side is lighter colored than the other. In water or 

 in a nutrient solution these spores germinate readily, as 

 seen in Fig. 78, the germinating tube appearing on the 

 light side of the spore. As these tubes grow, cross ]3ar- 

 titions (c, cl, /,) frequently appear, and sometimes the 

 peculiar little cells called sporidia are developed [a). 

 These sporidia might be called temporary spores, because 

 if placed in a nutrient solution, or manure water, they 

 grow something as spores do. Some authors have 

 claimed that on account of their presence in manure 

 applied to the land, oats may be infected with smut, but 

 this is disputed by Jensen and others. When massed 

 together the spores are of a dark, dusky brown color, 

 but when separated and viewed with the microscope 



