FUNGI IN GENERAL 107 



is in effect reducing it to a pabulum capable of supporting the 

 life of the Agaric which is to be developed from the mycelium. 

 All decayed wood is more or less penetrated by Fungus mycelium, 

 whether the Fungus itself is developed or not, the full develop- 

 ment depending upon a sufficiency of moisture, or other sur- 

 roundings. Doubtless continued moisture predisposes the wood 

 to decay, dissolves what is soluble, softens the cell walls, and 

 induces a kind of fermentation ; the growing mycelium does the 

 rest by slow disintegration and the liberation of the chemical 

 constituents, so that the main factor in the destruction of dead 

 wood is Fungus mycelium. The destructive process is extended, 

 in like manner, to dead leaves fallen on the ground, and con- 

 sequently continually moist, their final reduction to vegetable 

 humus being expedited by the growth of Fungus mycelium. 

 There are about 7 per cent of British Agarics which flourish 

 habitually on dead leaves or the dead stems of herbaceous 

 plants. We have computed that about 64 per cent of the 

 British Agaricini are terrestrial, or nominally so, but we cannot 

 separate those which flourish on old charcoal beds, on decaying 

 sawdust, or vegetable humus. Undoubtedly many of those 

 which grow ostensibly upon the ground thrive at the cost of 

 buried vegetable matter, the sites of decayed stumps, or frag- 

 ments of old roots. All we can claim for them is that all 

 these Agarics flourish upon their matrix, deriving their nourish- 

 ment from the substance upon which they grow, which must 

 be nitrogenous, and consist more or less of vegetable or animal 

 matter diffused through the soil, and not its inorganic con- 

 stituents. Of the residue of the Hymenomycetes little requires 

 to be said, since nearly all the Polyporei and most of the 

 Thelefliord grow on rotten wood, which is penetrated by the 

 mycelium. Need we mention two species as pre-eminent, 

 Polyporus hylridus and Mcrulius lacrymans, both known as 

 " dry-rot," which are in evidence for their power of destruction. 

 In addition to the Saprophytes are all those parasites which 

 attack living plants and compass their destruction. There can 

 be no doubt about the whole family of the Uredincae, the rust 

 and mildew of wheat, the hollyhock disease, the plum-leaf rust 

 — all determined foes of the plants upon which they flourish. 

 And there are upwards of twelve hundred different species 



