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greatest damage of all grain smuts in the United States. The disease 

 makes its appearance at the time of blossoming of the oat-plant, the whole 

 head becoming a dusty olive-brown mass. The infected flowers are 

 entirely destroyed by the disease and even the awns are affected. 

 In the Hidden Smut the spore mass is more or less concealed by an outer 

 membrane of the floral parts that remain intact from the disease. The 

 dusty mass is made up of great numbers of spores which are blown about 

 by the wind, some being caught in the open glumes of flowering oat-plants. 

 Since after blossoming the glumes close tightly about the ovary, such spores 

 are held imprisoned and remain so until the seed is in a condition to 

 germinate. Theu the imprisoned spores germinate after the manner of 

 several smuts, producing a three or four-septate promycelium, which usu- 

 ally bears oval or elliptical sporidia at the apex or laterally at the septa. 

 Infection threads are usually produced by these sporidia, but the promy- 

 celial threads may also produce them. These infection threads gain en- 

 trance to the host by piercing the delicate young cells of the first leaf- 

 sheath before the leaf has appeared. Plants are free from infection after 

 the growing leaves have pushed themselves as much as one c. m. through 

 the leaf-sheath. Brefield found by experimentation that oats germinated 

 up to 15° C. gave 3 per cent, smutted heads, but when grown at a higher 

 temperature give 1 to 2 per cent, smutted heads or more. 1 This bears out 

 ordinary experience that late sown oats while more liable to rust are 

 freer from smut. This immunity is probably due to the short period when 

 the plant is open to infection as a result of the rapid germination and 

 growth of the seed in the more favorable condition of temperature. 



In from thirty-six to forty-eight hours after infection considerable 

 mycelium will be developed which penetrates the first and second leaves 

 and gains entrance to the stalk or culm. It grows upward and invades 

 the young head in quite the same manner as in case of other smuts. In 

 place of a healthy head, a dusty mass of spores appears, which are scat- 

 tered to healthy heads by the wind. 



1. Brefield, O.. Recent Investigations of Smut Funsri and Smut Diseases. Trans 

 by Erwin P. Smith, Jour. Mycol. VI, pp. 1-3; 59-71; 153-164. 1890-91. 



