ON THE PREVENTION OF MILDEW IN PARTICULAR CASES. 205 



old cheese, may generate a mite ; and if the organs of a mite can be 

 thus formed, there could be little difficulty in believing that a larger mass 

 of decomposing animal matter might generate an elephant, or a man. 



The hypothesis therefore which supposes the various species of fungus 

 to spring from seeds, appears to me much the least objectionable ; and 

 if the minute bodies, which are supposed to be the seeds of these plants, 

 be really such, it will not be difficult to show that these are sufficiently 

 numerous to account, to a great extent, for the ubiquity of the plants they 

 are supposed to produce ; particularly as such apparent seeds, owing to their 

 excessive lightness, are capable of being everywhere dispersed by winds. 



A few vears ago I raised some mushrooms under glass with the intention 

 of collecting and subsequently raising mushrooms from the seeds they 

 might produce ; and I then endeavoured to ascertain the number which 

 would be afforded by a single fructification ; for a mushroom appears to 

 be nothing more than a fructification of the plant, though it is generally 

 spoken of as the plant itself. I placed thin plates of talc under a very 

 large mushroom at the period when the minute globular bodies, which 

 are supposed to be the seeds, first began to be disengaged from its gills ; 

 and I endeavoured to count the number which fell during each successive 

 hour, within the narrow field of a very powerful lens. The labour to my 

 eyes was, however, so severe, that I was unable to count with any 

 considerable degree of accuracy ; but the number which fell from a single 

 mushroom, within the succeeding ninety-six hours, exceeded, upon the 

 lowest calculation I could make, two hundred and fifty millions. I 

 endeavoured to raise mushrooms from these seeds, but I failed to obtain 

 any decisive results ; for though I readily procured mushroom spawn by 

 mixing such seeds with unfermented horse-dung, I also obtained it in 

 equal abundance, in some instances, where I had not introduced any seeds. 



Immense as the number of seeds produced by a single mushroom 

 appears, it probably is not much greater than that which a single plant 

 of mildewed wheat would afford ; and, according to this calculation, a 

 single acre of mildewed wheat would probably afford seeds sufficient to 

 communicate disease to every acre of wheat in the British empire, under 

 circumstances favourable to the growth of the fungus ; and I have never 

 seen a single acre of wheat, since the publication of Sir Joseph Banks's 

 pamphlet, so free from mildew but that it would have afforded seeds 

 enough amply to supply the adjoining hundred acres. There is also 

 reason to believe that the berberry-tree communicates this disease to 

 wheat ; and I have also often noticed a similar apparent parasitical 

 fungus upon the straws of the couch-grass, in the hedges of corn-fields. 



