156 Minnesota Plant Diseases. 



number of spores from its side or end. The thread thus con- 

 stitutes a basidium. In one of the smut groups the basidium is 

 not divided but consists of a single cell from the end of which 

 the spores are produced. These spores may be known as the 

 basidium-spores. They germinate immediately in warm, moist 

 conditions, by sending a fine thread, which seeks the host plant 

 and penetrates into the tissues, thus beginning the parasitic life. 

 If the basidium-spores are placed in a nourishing solution they 

 bud in yeast fashion and will so continue to do for an indefinite 

 period as long as the nutrient material is present. It is still 

 able to infect a host plant under proper conditions. 



The parasitic life usually begins in some young undeveloped 

 part of the host, e. g., the corn smut infects only young leaves 

 or young kernels of the corn. Here the parasitic mycelium 

 grows and builds itself up at the expense of the host plant. In 

 the oat smut the parasite gains entrance to the oat plant only in 

 the seedling stage of the latter. Now this penetration is accom- 

 plished in a peculiar way. In an oat field with smut the sound 

 grains of the oat become dusted with the spores of the smut 

 and thus at the seeding time in the spring the seed grains may 

 have spores on their surface. Now the conditions favorable to 

 the germination of the oats are also favorable to the germina- 

 tion of the smut spores and when the seedling oat appears 

 above ground there are also near by germinating basidium- 

 spores of the smut. The threads of these spores therefore 

 easily reach the young seedling and rapidly penetrate to the 

 growing-point of the stem, although this growing-point is hid- 

 den by the first leaves of the seedling. When the seedling 

 continues to grow, the parasite also grows, always remaining 

 in the growing point and forming patches of mycelium in 

 the growing points of all of the branches. The oat plants 

 thus affected do not appear very different from uninfected 

 plants until the grains mature. When the grains are still 

 very young the parasite invades all of them and here builds 

 up a dense mass of mycelium at the expense of the rich food 

 materials which the oat plant furnishes to the grains. At 

 the time when the oat grains are ripe the fungus threads 

 divide up into numerous cells and from each cell is formed 

 a spore, whose wall is at first gelatinous but later is black, 



