233 GRASSES OF IOWA 



Microscopic characters. — The powdery mass is made up of a 

 large number of very minute brown-colored spores with an 

 olivaceous tinge, especially when in masses. The spores are 

 somewhat variable in size, usually nearly round, or angular, 

 or elliptical. 



Germination of the spores — It is not difficult to obtain germi- 

 nating spores in sterilized water, but the process is slower 

 than in oats smut. In germination a tube (promycelium) is 

 pushed through the light colored outer wall of the spore (epis- 

 pore). Sporidia are not produced. In nutrient solution ger- 

 mination begios in fifteen hours, starting in the same way, but 

 more vigorous. Sometimes these become very long. The 

 segments frequently break up. 



OATS SMUT. 



Oat smut {Ustilago avenae (Pers.) Jensen), has long been 

 known to mycologists. Until the elaborate investigations of 

 Jensen- it was regarded as identical with that occurring on 

 wheat and known as (/stilago segetum. It was called Iredo 

 avenae by Persoon. f The literature is cited quite fully by Kel- 

 lerman and Swingle. X 



COMMON LOOSE SMUT OF OATS. 



The oats {Ustilago avenae (Pers.) Jensen), is affected by two 

 smuts; one is the common loose smut of oats {Ustilago avenae), 

 a disease long and well known to agriculturists. This smut 

 converts the flowers especially, the grain and adhering parts 

 to a black, powdery substance. It may affect all of the flowers 

 or only a part. 



In most cases it completely destroys the tissues of the spike- 

 lets, leaving a black mass of spores with threads and tissues 

 of the plant. The smut, during its early stages, is covered 

 with a membrane. The spores are free and form a dusty mass 

 of olive or dusky brown color; they are oval, sub-globose, ellip- 

 tical or somewhat angular, irregular or deformed, and light-^r 

 on one side; consents usually clear or slightly granular. The 

 outer wall or exposure is minutely warty. 



Germination. — The spores germinate readily in water; they 

 are said to retain their vitality for a number of years. We have 



*Le Charbon des Cereales. 4: 1889. 



+Syn. Meth. Fung. 224. 1801. 



+Rep. Kans. Agrl. Exp. Sta. 1889: 215. Bull. Kans. Exp. Sta. 8: 15. 



See also Bolley. Ball. North Dakota Agrl. Exp. Sta. 1: Arthur. 



Bull. Indiana Agrl. Exp. Sta. 35: Syll. Fung. 7: 461. 



