SURFACE MYCELIUM 99 



advantageous. In Coprinus sterquilinus it is particularly important 

 that the mycehum should spread itself as quickly as possible in a 

 dung-ball mass, for a single fruit-body is so large that its develop- 

 ment may exhaust the mycelium in from one to three balls. 

 A mycehum which does not succeed in occupying at least a certain 

 minimum volume of its substratum, as a rule at least one dung-ball, 

 remains sterile and does not develop the reproductive apparatus. 

 For this reason it is not surprising to find that the mycehum of 

 Coprinus sterquilinus has a particularly rapid rate of surface growth 

 over its substratum, much more rapid than that of the myceha of 

 smaller Coprini with which it so frequently has to compete. It may 

 be added that the surface growth observed in sterihsed cultures 

 also takes place in unsterihsed horse-dung balls which have become 

 naturally infected, and which have subsequently been placed under 

 moist conditions in the laboratory. From such material I have 

 been in the habit of procuring the fungus in the first place, and 

 therefore have often had occasion to watch for the first signs of its 

 appearance. These first signs are always the rapidly-growing 

 surface hyphae. 



In a dish-culture containing sterihsed horse-dung balls inocu- 

 lated above with spores it invariably happens that the mycehum, 

 on arriving at the base of the balls as a result of superficial growth, 

 continues to grow for some centimetres over the bottom of the 

 dish in the film of moisture there present. Under natural con- 



FiG. 56. — Coprimis sterquilinus. A mature fruit-body coming up from the base of 

 a horse-dung ball in a pure culture in a large crystallising dish. A thin and 

 characteristic white layer of mycelium coats each dung-ball. The fruit-body 

 is held in its upright position : in part because the lower end of its stipe is 

 attached to the under side of a dung-ball by hyphal strings and the layer of 

 mycelium already mentioned ; in part because the base of its stipe rests on the 

 bottom of the dish ; in part because its stipe, a little way above its base, is in 

 lateral contact with two dung-balls, and in part because the ceritre of gravity 

 of the whole fruit-body is almost vertically above the centre of its base. The 

 pileus is still expanding. Its edges have become torn into rays which are 

 becoming revolute. The middle of the spore-discharge period has come, and 

 many millions of spores are being liberated. The pileus is black because a 

 dark-brown pigment is present in the cells of the pileus-flesh, the trama, and 

 the hymeniimi and because the hymenium on every gill bears jet-black spores. 

 The blackness of the upper portion of the stipe is due to the presence in 

 the cells of the same dark-brown pigment that occurs in the pileus, and not 

 to the deposition of spores. A spore-deposit has already darkened the 

 upper edge of the dish on the left and the layer of mycelium on the tops of 

 dung-balls in the back-ground. Reduced to about two-thirds the natural 



size. 



