MILDEWED WHEAT. 373 



sown wheat. At a quarter past five, all the three indicated 

 29 J. The sun was then a little above the horizon, and 

 obscured by a small cloud ; the sky was clear, the air still, 

 and mild to human feeling. In the same situation, the ther 

 mometers, at eight o clock, indicated 55, and at two p. M. 

 75. At ten in the evening, the thermometer, four feet from 

 the ground, stood at 44, and the one on the grass, at 42. 

 At half-past four on the morning of the 21st, the thermome 

 ter, four feet from the ground, stood at 34, one on the grass, 

 at 28|, and one on the wheat, at 29. The thermometers 

 on the grass and wheat were thinly coated with ice, and the 

 morning was clear and agreeable. The formation of dew was 

 not very copious on either of the mornings, and my reapers 

 made no remark about cold or frost when handling the 



c5 



grain. The field of spring-sown wheat, already mentioned, 

 and one of barley, were at this .time in a green state, and 

 very promising ; but the grain made no farther improve 

 ment, and mildew appeared on both crops in a day or two 

 afterwards. 



Although I have not been able to produce mildew by arti 

 ficial means, the observations made with the thermometers in 

 1830 almost amount to a demonstration of its origin. Every 

 case of mildew, whether general or partial, in a district, may 

 be accounted for by cold produced by the radiation of heat, 

 coupled with the state of the crops ; and the hypothesis has 

 been strongly supported by Scottish writers on practical hus 

 bandry, Brown and Aiton, while recording, as the cause of 

 mildew, natural phenomena which result from or generally 

 accompany the radiation of heat. 



But from whatever cause mildew may proceed, there is no 

 question of the wheat crop, throughout a considerable extent 

 of North America, being liable to its effects. Many instances 

 of mildew are recorded in my tour ; and I scarcely passed 

 through a district, the surface of which consisted of sudden 

 undulations, or small forest clearances, where the wheat was 

 not seriously injured by it. Some accounts which I have 

 received from parts of Upper Canada for 1834, allude to the 

 destruction of wheat by frost. In all partially cleared parts 



