BLACK BLIGHT IN WHEAT. 163 



consequently will be starved. Whilst the season 

 continues dry and cold, the exuded sap will re- 

 main like dry gum ; but as it advances, and the 

 weather becomes warm and moist, the gum be- 

 comes moist, soft, and putrefying ; and then 

 forms, and affords a nutritive bed for the mould 

 or fungus ; which grows and increases until 

 it is deprived of moisture, or is so reduced as 

 to be insufficient to sustain it, when it dies ; and 

 according as the season is favourable or un- 

 favourable to its growth, it produces a brown, or 

 black powdery substance, in a proportional quan- 

 tity. Thus then, the foundation or cause of the nust 

 or fungus, is the putrefying matter discharged 

 from the ruptured sap-vessek of the plant : and 

 although the ruptures may be occasioned by a 

 contraction or obstruction of the vessels by 

 atmospheric influence ; the overfulness, or over- 

 luxuriance of the plant, produced by surfeit ; or 

 the being glutted with rank and unwholsome 

 food ; and its incapacity of digestion, and un- 

 healthy obstructions ; renders it more liable to 

 such injuries : and may therefore be considered 

 as the general cause of the disease, blight, or 

 rust. 



I have planted wheat in a rank compost of 

 dung, which from its first appearance in the 

 autumn, during its growth in the winter, and 



M 2 



