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XX. On the Prevention of Mildew in particular Cases. By 

 Thomas Andrew Knight, Esq. F.R.S.fyc. President. 



Read 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 pro- 

 cesses, 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, (Bo- 

 letus lacrymansj 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 



* Quarterly Review, Vol. vii. page 33. 



