504 SPECIAL PLANT PATHOLOGY 



germ-pores. The teliospores are unicellular. As a remedial measure 

 the use of tobacco water or Bordeaux mixture is recommended. 



Com (Zea mays, L.) 



Dry-rot (Diplodia zem (Schw.), Lev.). — The dry rot fungus attacks 

 the dry ears of corn soon after silking and does not usually manifest 

 itself until husking time, when the kernels are found to be covered with 

 a whitish mycelial growth, which dips down between the individual 

 grains of corn. The grains so attacked become shrunken, loosely 

 attached to the cob, lighter in weight, darker in color, and more brittle 

 than the healthy grains. Pycnidia may be found imbedded in the 

 mycelium, especially between the kernels. In the open field, these 

 pycnidia may be formed in such numbers as to impart a black color 

 to the grains of corn. Of course the feeding value of the corn is gone 

 and some physicians even ascribe pellagra to the use of such moldy 

 corn. When the fungus attacks the stalks, it forms small dark specks 

 under the epidermis near the nodes and even on three-year-old stalks 

 pycnidia have been found. Infection takes place through the roots 

 and the fungus which enters in this way finally reaches the stem. Ear 

 infection may also occur through the silk by wind-blown spores which 

 come from old diseased stalks left in the field, so that by destroying 

 the corn trash the disease can be controlled to some extent. Rotation 

 of crops is probably more efiicacious. 



Smut {Ustilago zea (Beckm.), Unger). — The smut boils of Indian 

 corn, or maize, are found not only on the ears as with most smuts, but 

 also on the husks, on the tassels of male flowers, on the leaves, and even 

 on the stem (Figs. 179 and 180). The attack first begins on any young 

 and tender part of the plant. If the leaves are the part attacked, they 

 assume a pale yellow hue and are puckered with smaller, or larger 

 bladder-like swellings. The swellings are made up of masses of the 

 hyphae of the smut fungus and their surface is covered with a smooth 

 skin-like covering. Later the hyphae divide up into innumerable 

 rounded cells, which develop into the smut spores, or chlamydospor.es. 

 Finally, the silvery-white skin having been more and more stretched 

 bursts, and the black chlamydospores are set free, as a powdery 

 mass. The echinulate chlamydospores measures 8 to 12/u, and they 

 readily germinate in manure-water giving rise to a four-celled basidium, 



