296 



Minnesota Plant Diseases. 



saprophytic stage, beginning with the germination of the spore 

 and ending with the formation of an infection tube by the sec- 

 ondary and tertiary spores. 



The secondary and tertiary spores, produced by the smut 

 spore, are capable of living in a nutrient solution or in fresh 

 manure, where they may form a saprophytic mycelium or may 

 continue to bud off more spores in a yeast-like fashion. They 

 may live thus for years, and when finally brought into contact 

 with the seedling plant, they may still cause infection. 



FIG. 147. Stinking smut of wheat. 1. A head of wheat with smutted grains (smutted 

 grains are colored black). 2. Small portion of a head showing smutted grains which 

 are fissured, and show the black spore mass within. 3. Isolated grains which are 

 smutted and have fissured walls. One grain is sectioned. 4. Smut spores germinated 

 and producing at the end of the germ tube long, needle-like spores, which sometimes 

 fuse together in pairs by cross-threads as shown on the left. 5. The thread spores, 

 shown in 4, in germination sometimes again producing secondary spores. 6. Smut 

 spores germinating to long infection threads without first forming spores. 4-6 highly 

 magnified. After Tubeuf. 



The treatments used for loose smut of oats are also effective 

 against this disease. The Jensen hot water method (see chap- 

 ter on Prevention), has been found useful, but the most effective 

 and easiest method is the formalin treatment, which has practi- 

 cally supplanted the former. This smut can in practice be en- 

 tirely prevented by this method. 



