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XXVII. ON THE PREVENTION OF MILDEW IN PARTICULAR CASES. 

 [Read before the HORTICULTURAL SOCIETY, May 4, 1813.] 



THE little pamphlet upon the rust, or mildew, of wheat, for which the 

 public are indebted to the patriotic exertions of the venerable President 

 of the Royal Society, affords much evidence in proof that this disease 

 originates in a minute species of parasitical fungus, which is propagated, 

 like other plants, by seeds ; and the evidence adduced would, I think, 

 be sufficient to remove every doubt upon the subject, were the means 

 ascertained by which the seeds of this species of fungus are conveyed 

 from the wheat-plants of one season to those of the succeeding year. 

 This, however, has not yet been done ; and therefore some persons still 

 retain an opinion that the mildew of wheat consists only of preternatural 

 processes, which spring from a diseased action of the powers of life in the 

 plants themselves. 



An hypothesis, which differs little from this, has been published in the 

 present year respecting the dry-rot (Boletus lacrymans) of timber *. It is 

 contended that the different kinds of fungus, which appear upon decaying 

 timber of different species, are produced by the remaining powers of life 

 in the sap of the unseasoned wood ; and that the same kind of living 

 organisable matter, which, whilst its powers remained perfect, would have 

 generated an oak-branch, will, when debilitated, give existence to a 

 species of fungus. But, if this power exists, and becomes capable, during 

 its rapid declension, of deviating so widely from its original mode of 

 action, the species of fungus it would produce might be expected to 

 become successively more feeble and diminutive ; whereas the most robust 

 and gigantic of the whole genus, the Boletus squamosus. springs from wood 

 when that is in its last stage of decay; and the best known, and the 

 most valuable species to mankind, of this tribe of plants, the common 

 mushroom, appears as obviously to spring from horse-dung, under 

 favourable circumstances, as any species of the same tribe appears to 

 spring from decomposing wood, without the previous presence of seeds f. 

 Yet it can scarcely be contended that any vital powers, capable of 

 arranging the delicate organisation of a mushroom, can exist in a horse- 

 dung ; and the admission of any such power would surely lead to the 

 most extravagant conclusions. For if a mass of horse-dung can generate 

 a mushroom, it can scarcely be denied that a mass of animal matter, an 



* Quarterly Review, Vol. VII. page 33. 

 t See Nicol's Forcing, Fruit and Kitchen Gardener, 4th edition, page 119. 



