64 On tlte Rust or Mildew. 



seed) are objects of culture, there is only wanted a degree of vigour 

 and luxuriance in the plants, sufficient for that purpose ; and if the 

 fertility of the soil be raised to a much higher pitch than is necessary, 

 or consistent with that object, injurious, rather than beneficial conse- 

 quences may be the result *. Land may be roo rich for corn crops, 

 and it is better to keep it in a well-balanced condition, or in a medium 

 state of productiveness, than in too fertile a state f. A superabundant 

 quantity of sap and juices, in vegetables growing on highly cultivated 

 lands, it is evident, must necessarily render them more susceptible of 

 the effects of sudden and extreme changes, and consequently more 

 liable to disease. Besides, as mushrooms are produced on beds of 

 dung, great quantities of manure must promote the growth of fungi, 

 or parasitical plants, on the crops of wheat, if they are once infected. 

 The wheat produced on the site of a dunghill, is always rusted, even 

 in the most favourable seasons ; and if the whole field is a species of 

 dunghill, how can it escape f ? The whole fungus tribe are seldom 

 seen to grow, but from superfluous vegetable matter, as rotten wood, 

 thatch, decayed hay, or some light rich substance, aided by a certain 

 degree of heat and moisture ; and there is no substance more analo- 

 gous to such a production, the offspring of corruption, than dung. 

 This may be regarded at least, as a proximate, or predisposing cause. 

 If the seeds of the fungi float in the atmosphere, they may more 

 easily find a nidus, on too succulent and lusty growing plants, the 

 substance of which is in a tender state, and the pores more dilated, 

 than in the hard straw produced by a compact soil . 



A too frequent repetition of crops of wheat, more especially when 

 accompanied by great quantities of manure, to force a crop, or raised 

 on soils unsuitable to the growth of that crop, will often have the 

 same effect. The rust was but little known in the western, or the 

 northern parts of England, or the southern counties of Scotland, un- 

 til of late years, when every exertion has been made, to increase the 

 quantity of that grain. Even clay lands, so congenial to wheat, have 

 been injured by such severe cropping ; but on weaker soils, as sandy 

 and calcareous loams, the plant has suffered, in respect both of quan- 

 tity and quality. 



It is well known, that loose and open soils, such as turnip lands in 



* Hence the great advantage of having previously a green crop, to absorb 

 the superabundant and injurious richness of the dung. 



f Communication from Dr Coventry. It is stated in a letter from Mr Wm. 

 Scott of Horncastle, ( Farmer's Journal, Nov. 20. 1815), " That wet falling 

 on soils full of manure, causeth too luxuriant a growth of corn, from whence 

 springs mildew." This doctrine is sanctioned by the authority of Parmentier, 

 who ascribes the rust, " a I'abondance d'un sue nourricier, resultant d'une 

 vegetation trop vigoureux, plutot qu'aux brouillards, qui n'y ont aucun part 

 directe. Traite sur la Culture de Grains. " Vol. i. p. 242. 



\ Communication from John Middleton, Esq. 



It is remarked by Mr Holdich, that the disease is generally in proportion 

 to the broadness of the leaf; that it first takes place upon the upper leaf or 

 sheath, out of which the ear issues. When this is narrow, small, and early wither- 

 ed, there is little danger from rust. Those broad leaves ought, if possible, to be 

 got rid off, which perhaps may be effected, when the crops arc drilled. 



