THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL, 



Vol. IX. JULY, 1888. No. 7. 



Smut of wheat, oats, and barley.* 



Ustilago carbo. Tul. 



Even the most unobservant person who has walked through a field of wheat, 

 oats, or barley must have noticed smutted ears. Instead of the healthy spike or 

 panicle of grain, sooty and ragged masses of black dust and scales are seen 

 surmounting the fruiting stems of the corn. In some places the disease is 

 called ' chimney-sweeper,' in others ' black-ball,' ' dust-brand,' or ' smut.' In 

 certain districts it is erroneously termed ' bunt,' which is a totally different 

 disease of corn. The black powder is produced in such profusion that it is 

 impossible to gather a few diseased ears without the hands being soiled as if 

 with soot. We have heard smutted ears called ' the male flowers of corn,' 

 the erroneous idea being that these diseased ears ai^e the black pollen-bearing 

 plant. Some districts are more liable to smut than others, although none 

 are free. At times the disease is extremely destructive, especially in oats. 

 In some instances nearly the whole crop becomes smutted, and in bad cases 

 from one-sixth to one-third of the crop is destroyed. When smutted wheat 

 is gi'ound with sound grain it not only discolors the flour but injures it as 

 food. Straw infected with the black powtler or spores of the fungus are dis- 

 liked by cattle, and it is an oflensive adjunct to chaft' when given in food to 

 the animals. 



The smut disease of corn is caused by the presence of a fungus which ex- 

 ists within the tissues of the plant, grows with the growing stem, and at last 

 bursts from the inside of the plant outwards at about the time when the corn 

 is reaching maturity. The name of the fungus is Ustilago carbo. The name 

 is derived from Ustio, a burning, and carbo, charcoal ; having direct refer- 

 ence to the burnt and sooty appearance. 



A close examination of the extremely curious fungus which causes smut 

 shows how it invades the corn. If we take smutted ears of wheqt and oats 

 and examine them without a glass we shall see them as at a and b. The first 

 point to be specially noted in the field is that every ear w^hich springs from 

 one root is smutted. This fact indicates that the disease springs from the 

 base and runs up every stem from the ground line. A further proof is that the 

 lowermost part of the ear is the part that first shows the disease. It is com- 

 mon to see the bottom of an ear of wheat or barley or of a 2Danicle of oats 

 badly smutted and the top sound. The disease in these instances has not 



Explanation of the Plate. 



a. The smut fungus, Ustilago carbo. Tul., in wheat. /,g, h, i. Spore of Ustilago, germinating, magnified 



b. The same in oats. i,ooo diameters. 



c. Spores of Ustilago, magnified 400 diameters. tn, n. Growth of hyphae in Ustilago, magnified 1,000 



d. Spore of potato fungus, magnified 400 diameters. diameters. 



e. Spore of onion fungus, magnified 400 diameters. 



' From Journal of Microscopy and Natural Science, April, 18 



