380 Journal of Agricultural Research voi. xvm, no. 7 



Nobbe (2j), in 1897, dried rye grain at 80° C. for several hours with 

 very little effect upon subsequent germination. More severe exposure 

 to dry heat was found to injure seriously the germinability of rye, while 

 wheat and oats were killed at shorter exposures. 



Jodin {16), 1899, reports that if seeds of peas and cress are dried at 

 60° C. for 24 hours they can endure dry heat at 98° C. for 6 hours without 

 injury, while similar seeds heated in humid air at 40° C. for 20 hours lose 

 their viability. 



Dixon (7, <?), in 1901 and 1903, found that if various kinds of seeds were 

 previously dried over sulphuric acid in a desiccator they could withstand 

 exposure to 95° C. for several days without losing their viability. He 

 reports that well-dried seed will endure even somewhat higher tempera- 

 tures, that is, 110° to 120° C, without injury. 



Schneider-Orelli (25, 26), 1909 and 1910, Neuberger (22), 1914, Wag- 

 goner (29), 1917, Harrington and Crocker (13), 1918, and others (5, 6, 

 II, 12), working with various seeds, have confirmed, in general, the 

 results of former investigators — that various seeds are able to endure 

 high temperatures, especially when their moisture content is low. 



It was not until about 1900, however, that plant pathologists began 

 to appreciate the possibility of using dry heat as a means of control for 

 certain seed-borne diseases. 



In 1908 there appeared almost simultaneously several papers on the 

 subject of smut control by dry heat. Kiihle (19) reported that the 

 spores of stinking smut are killed when exposed to 65° C. for 12 minutes 

 and that loose smut also can be controlled by dry heat. For barley he 

 used temperatures up to 90° C. and for wheat up to 110° C. without 

 destroying the viability of the seed. The barley treated in this way 

 was free from loose smut, but the results with wheat were not so suc- 

 cessful. While Kiihle does not mention the length of time during which 

 theseed was treated, it probably is the same as that reported the same 

 year by Stormer (27), who worked with him. Stormer used samples 

 which were first dried at low temperatures and then heated for 10 min- 

 utes at each of the following temperatures: 50°, 65°, 75°, and 90° C. for 

 barley and 50° to 60°, 65°, 85°, and 100° to 110° C. for wheat. The 

 samples were then cooled down to room temperature after each lo-minute 

 heat treatment. The results showed a marked decrease of smut in barley 

 and only a slight decrease of smut in wheat. 



For several years following 1 908, dry heat treatments were abandoned 

 by plant pathologists for a modified heat treatment in which seeds were 

 first soaked in water and then subjected to high temperatures. This 

 method was used with some success by Appel (/), Appel and Riehm 

 (2, 3, 4), Gisevius and Bohmer (10), Lang (20), Stormer (28), and 

 Westerdijk (jo) for smut control. For example, Appel and Riehm 

 (2, 5) soaked smutted seeds of barley and wheat in water for 4 hours 

 and then heated them at 55° to 60° C. for 20 to 30 minutes. These 



