4- On Blight in Wheat, 



minute and volatile seeds may be said to be every 

 where present, ready to produce their kind, wherever 

 they may find a genial matrix. Such at least appears 

 to be the nature of the fungus, or fungi, of wheat ; for 

 it may be liable to the attack of more than one species. 

 In a warm drj^ summer, which is well known to be fa- 

 vourable to the health, vigour, and productiveness of 

 the wheat crop, the seeds of fungi are harmless, so long 

 as the fine weather continue. On the contrary, in a 

 cold wet season which gives languor and weakness to 

 the wheat plants, few crops escape entirely their de- 

 structive effects. A standing crop not unfrequently 

 escapes, while plots that are lodged in the same field, 

 especially in pits and hollow places, become liable to 

 their attack. Even strong healthy crops may in a few 

 days or perhaps in a few hours, be rendered liable to 

 be assailed, not progressively, as by infectious disease, 

 but at once, as by a blast or blight. In the state of the 

 atmosphere we are to look for the cause of the disease 

 in a standing crop ; and nothing is so likely to bring on 

 the fatal predisposition of the plants, as a succession of 

 cold rains while the grain is forming. The coldness 

 necessarily gives a check to the rich saccharine juices 

 which are then rising towards the ear, and the moisture 

 may, at the same time, assist the seeds of the fungi to 

 germinate and take root." In support of his opinion, 

 Mr, Marshall adduces the following facts. "In 1804 

 (a very dry season) the disease was almost universal in 

 England, except in two counties. The cause of the 

 disease, in the county in which he had the best oppor- 

 tunity of observing it (Caermenthshire) appeared very 



