306 



GENERAL MORPHOLOGY OF PLANTS 



Fig- 253- 

 .ut (Ust 

 affected ear, stalk, and 



Corn smut (Ustilago zeac), 

 I blades. 



down between the young blades at the end of a growing corn stalk 

 they germinate, producing a germ tube which enters the tissues of 

 the corn plant and about six or eight weeks later produces the 



smut masses again. The infection is 

 local in the case of the corn smut, any 

 of the embryonic tissues of the corn 

 being susceptible if the germinating 

 sporidia are present. The infection 

 which produces the smut at the lower 

 joints of the stalk takes place earlier 

 than that in the ear or that on the 

 tassel. The corn smut is often relished 

 by cattle, and does not seem to injure 

 them unless they eat too great a 

 quantity. 



458. Othes species of smut. 

 Other examples of smut are the loose 

 smuts on the grains, as the loose smut 

 of oats (U. avence), the loose smut of wheat (U. tritici), and the 

 loose smut of barley (U. nuda). The only part of the host 

 injured is the flower, the young kernels (ovary) and parts of the 

 palets being reduced to a black smutty mass consisting of disin- 

 tegrated parts of the flower, the mycelium, and the spores. 

 They are called loose 

 smuts because the mass 

 of spores not being 

 covered, even by any 

 delicate membrane, the 

 spores are easily scat- 

 tered. Although only 

 the flower parts are in- 

 jured, the mycelium 

 travels all through the 

 host while it is growing, from the seedling up to the full- 

 grown plant. The method of infection is very interesting. In 

 the case of the oat plant the smut spores clinging to the seed oats 



Fig. 254. 



Corn smut, spore germinating and producing sporidia. 

 At the right, sporidia budding and producing secondary 

 sporidia. (After Brcfcld.) 



