100 RESEARCHES ON FUNGI 



ditions, this extension of the mycehum beyond its nutrient sub- 

 stratum doubtless often serves to bridge the gap which may exist 

 between one dung-ball and one or more of its fellows as they lie 

 upon the ground in fields, etc. : it may permit the mycelium in one 

 ball to infect another ball by growing to it via the surface of the soil 

 or grass-stems. The aerial hyphae which project from the surface 

 of a ball to a distance of a few millimetres may be of advantage in 

 extending the mycehum across air-gaps between nearly touching 

 balls. In dish-cultures I have often noticed the spread of the 

 mycelium from ball to ball in this way. When this has occurred, 

 the aerial bridging hyphae finally become reduced to a few thick 

 mycelial strands. These strands are channels of conduction, and 

 make it possible for a fruit-body which has arisen on one ball to 

 drain the mycelial contents of several balls, and thus to obtain the 

 full quota of materials necessary for its construction. ^ 



The surface mycelium, when it first makes its appearance at the 

 surface of dung, consists wholly of loose hyphae ; but, after a few 

 days of growth, it forms a dense white membranous covering which 

 adheres closely to the exterior of each infected dung-ball (Figs. 56 

 and 58) ; also Vol. Ill, Fig. 71, p. 182). Whilst this change is 

 going on, the older aerial hyphae disappear, and it may be that 

 their contents are withdrawn to be used up by the hyphae forming 

 the membrane. The membrane, as a rule, is not uniform in texture 

 but comes to contain, or even to be chiefly composed of, conducting 

 strands (Fig. 54, p. 95). Along these strands, doubtless, some of 



1 The surface hyphae of other saprophytes, such as Moulds and wood-destroying 

 Hymenomycetes, function in a manner similar to those of Coprinus sterquilinus, 

 i.e. by hastening the occupation of the substratum when continuous and by bridging 

 gaps between portions of it when discontinuous. In this connexion the case of 

 Merulius lacrymans, the Dry-Rot Fvmgus, may be cited. Often, in damp cellars 

 in England, the mycelium of this fungus grows out from a wooden beam on to the 

 brick wall and spreads over the wall for a distance of several inches or feet. In so 

 doing, it may encounter other pieces of wood which it then proceeds to infect. Once, 

 in the cellar of a private house at Edgbaston, Birmingham, I observed that the 

 mycelium had spread from a beam downwards over a perfectly bare white-washed 

 wall for a distance of three feet (c/. these Researches, vol. iii, 1924, pp. 41-42, Figs. 23 

 and 24). There can be no doubt that, for Merulius lacrymans, the surface growth 

 of the mycelium on non-nutrient substances, which gives the fungus the advantage 

 of extending its area of attack, contributes in a marked degree to the destruction 

 of the wood-work in houses. 



