198 BACTERIA IN RELATION TO PLANT DISEASES. 



Many experiments have been made with grains to free them from smut fungi and in 

 this way considerable knowledge has been gained respecting the toleration of seed wheat, 

 oats, etc., for hot water, copper salts and various other disinfectants. Some of the leading 

 papers are mentioned under Literature. Only a few of the results will be cited here. 



Jensen who discovered the hot-water treatment for stinking smut (1888) advised 

 temperatures between 127 and 133 F., and exposures of seed wheat and oats for not over 5 

 minutes. He did not, however, determine accurately the thing we are here specially inter- 

 ested in bringing out, namely, the killing temperature for the grains. 



In 1890, Arthur determined the effect of hot water on the germination of wheat. 

 Wheat seeds immersed 5 minutes in water at 135 F. (57 C.) are not injured. Six hundred 

 seeds exposed to 130 F. (54 C.) for 10 minutes also gave excellent results on germination 

 12.5 per cent in 24 hours and 93 per cent in 5 days. The injury to those treated 10 minutes 

 at 135 F., and 5 minutes at 140 F. (6o C.) equaled about 20 per cent. The limit of germ- 

 ination is 150 F. for 5 minutes (t,^ P^ r cent). No germinations were obtained when wheat 

 seeds were exposed to higher temperatures, e. g., 155 F. for 5 minutes, or to 150 F. for 10 

 minutes. 



In 1 89 1 Arthur tested the effect of hot water on oats, with especial reference to the 

 prevention of loose smut. He states that the hot-water treatment 10 minutes in water 

 at 135 F., or 5 minutes in water at 135 F. to 140 F. (57 C. to 6o C.) entirely destroys the 

 smut while at the same time it improves the growth and increases the yield of oats. The 

 water may be even as hot as i45F. when the oatsare first put into it without much injuring 

 the germination. Arthur made the exposures in cheese-cloth bags. 



Latta found 5 minutes' exposure of oats in copper sulphate water (1 pound to 1 gallon) 

 destroyed the smut but the germination was slower and the yield per acre was reduced. 

 The comparative yields were: Hot water, t,^ bushels; untreated, 28 bushels; coppered, 

 24 bushels. Arthur, who reports this, tested the effect of copper sulphate on germination 

 on lots of 200 seeds and obtained in the germinating chamber the following per cents : Hot 

 water, 99; untreated, 98; copper sulphate, 67. Even in the soil where 98 per cent of the 

 oats treated with copper sulphate finally germinated, they did so very slowly, the primary 

 roots were often killed, and often they pushed out the plumule in advance of the roots. 



Kellerman & Swingle (1890) found that exposure of wheat at 139 to 140 F. for 15 

 minutes destroyed nearly all of the kernels, i.e., on a plot that should have yielded 3,000 

 or more heads there were only 9. Copper sulphate 8 per cent, 24 hours, limed orunlimed, 

 reduced the germinations about one-fourth. Copper sulphate 5 per cent 24 hours, unlimed, 

 reduced the yield nearly one-third. Bordeaux mixture reduced the yield over one-fourth. 

 Eau celeste, 24 hours (on another page the time is said to have been 36 hours) destroyed all. 

 Carbolic acid 5 and 10 per cent for 20 hours destroyed all. Mercuric chloride 1 per cent 

 for 20 hours destroyed all. Potassium bichromate 5 per cent for 20 hours destroyed about 

 half. 



According to Kellerman & Swingle (1891) oats which were treated at 141. 8 F. (6i C.) 

 for 5 minutes gave a good crop. The same result was obtained by exposing at 138.2 F. 

 (59 C.) for 10 and for 15 minutes, i.e., there was no destruction of the seed. Potassium 

 sulphide 0.75 per cent and 0.5 per cent for 24 hours reduced the number of stalks about one- 

 fourth. Copper sulphate 0.1 per cent for 24 hours reduced the number of heads about one- 

 fourth. Copper sulphate 0.5 per cent for 24 hours reduced the number of heads nearly 

 half. Copper nitrate in 5 per cent solution for 24 hours, limed or unlimed, destroyed most 

 of the seeds. Even 2.5 per cent or 1 per cent greatly reduced the crop. Corrosive sublimate 

 0.1 per cent for 24 hours reduced the yield three-fourths. Potassium bichromate 10 per 

 cent for 23 hours killed all; same, 1 per cent for 9 hours, reduced the crop one-half or more. 



They recommend treating oats for smut by (1) hot water: temp. 132. 5 F., time 15 

 minutes; or, (2) potassium sulphide: 1 pound to 20 gallons of water, time 24 hours. 



