FUNGI AFFECTING OATS 



The Loose Smut 



Ustilago arence 



Some estimates of the loss due to this fungus have 

 already been given in the Introduction (p. 2). A good 

 representation of its appearance is seen in Plate XVII. 

 The black masses consist of millions of minute spores, 

 by means of which the fungus reproduces itself. The 

 spore masses ripen about the time the oats are in bloom, 

 when the cliaif enveloping the embryo seed is spread 

 wide open. The spores are blown over the field, and 

 many of them lodge on the inner side of the chaff parti- 

 cles, where they remain as the seed ripens, and are not 

 dislodged when it goes through the threshing machine. 

 The smut spores are also largely distributed from the 

 smutted heads and lodged in the chaff of sound kernels 

 during threshing, although it is probable that only a 

 small percentage of them get far enough into the chaiBf 

 to infect the plants that develop from the kernels. 



After the spores have lodged in the chaff they re- 

 main there until the oats are i:»lanted. Then they ger- 

 minate by sending out little tubes, which enter the 

 young plant through the first leaf-sheath. These tubes 

 are only able to gain access to the plants during a very 

 short period of the growth of the latter. After the oats 

 have pushed out the second leaf the danger of infection 

 by smut is past. When the germinating tube has entered 

 the plant it sends out branches in all directions, pene- 

 trating the stem and all its parts, thus forming the 



187 



