Feb. 3. 1919 Physoderma Disease of Corn 143 



stimulating effect caused by the presence of the invading fungus. A few 

 days later these spots are dark brown in the center, owing to the forma- 

 tion of the dark brown sporangia of the fungus. This change in color 

 spreads until the entire spot is a dark or chocolate brown. These infec- 

 tions are often so abundant as to coalesce, and sometimes the entire 

 sheath may become brown (PI. 10). Where the infections are as numer- 

 ous as this, the entire leaf often is killed before the plant is mature. 

 However, the disease is usually more abundant on the parts of the sheath 

 which are beneath the overlapping parts where the moisture is held. 

 The disease often is accompanied by a reddening of the sheath and mid- 

 rib, and especially the latter, which may almost entirely mask the brown 

 spots. After the plants begin to mature, the epidermis becomes loose 

 over these areas and they appear as brown blisters. This dry epidermis 

 breaks easily and the spores are liberated as a brown spore dust. The 

 entire parenchyma tissues of the invaded parts are destroyed by the 

 disease, leaving the vascular system as so many free threads after the 

 spores have been liberated (PI. 11, C, E). On the culms the spots are 

 very much like those on the sheath and midrib. They are usually more 

 abundant at the nodes and just below the nodes, where spores are more 

 hkely to lodge and where free water is held by the sheath. The culms 

 often are completely girdled at the nodes and are very easily broken by 

 the winds after the tissues have been invaded. The disease is responsible 

 for considerable lodging of corn in the South in the early stages of matur- 

 ity. Only the lower nodes as a usual thing become so thoroughly in- 

 vaded by the fungus as to be easily broken (PI. ii,A,B), Considerable 

 damage may result from severe attacks of this kind. After the plants 

 have fallen, the pith at the infected nodes will be found to be filled with a 

 brown mass of spore material (PI. 1 1 , D) . 



The signs of the disease on teosinte (Eicchlaena mexicana) are very 

 similar to those on corn, and therefore a separate description will not be 

 necessary. 



The pronounced signs of the disease have led farmers to apply various 

 significant terms to it in the way of common names. The writer has 

 heard the following names applied to it: " Rust," "corn measles," "corn 

 pox," "dropsy," "frenching," and "spot disease." None of these terms, 

 however, is in general use, and some of them — for instance, "rust" and 

 "frenching" — would be incorrect, as corn is known to be affected by 

 other distinct diseases called by these names. The name "falserust" 

 has been suggested as a desirable common name for the disease. There 

 would be a strong tendency, however, on the part of the layman to drop 

 the word "false," thus causing a confusion with the true rust. Further- 

 more, the disease on the sheath and the culm bears very little resemblance 

 to a rust. Since no satisfactory term suggests itself at present and since 

 the scientific term " Physoderma," seems to be gaining favor as a common 

 name, the author suggests that this tenn be retained. 



