60 THE EVOLUTION OF CONTINUITY 



If one soaks a piece of bread in water and covers it with 

 a glass dish, a good growth of Mucor is sure to develop within 

 a few days. At first it appears as white dots on the surface 

 of the bread, resembling moist spots of uncooked flour. 

 Each of these spots is a growing " mycelium " or network 

 of mould which has originated from a spore — millions of 

 which are everywhere about in the air and dust ; and thus 

 each mycelium is only a part of a Mucor Individual, though 

 several Individuals may have been involved in the production 

 of the spores producing the mycelia. 



For a day or two appearances remain more or less the 

 same except for the extension of the mycelia, then with 

 startling suddenness the bread becomes covered with a white 

 swansdowny growth of exquisite fineness, which close inspec- 

 tion shows to be composed of innumerable branching threads 

 like the finest spun glass, while scattered over the surface 

 are minute white dots. This is due to the development of 

 aerial branches which are produced with the view to forming 

 spores, the white dots being the " sporangia," or little cases 

 full of spores, at the tips of the aerial branches or " hyphae." 

 The spores are produced in enormous numbers, and every 

 one which falls into a suitable environment can originate a 

 new mycelium. 



Within a certain time the fluffy mass of mould, composed 

 of how many mycelia it is impossible to say, so close is the 

 interweaving, begins to look as if fine soot had fallen on it ; 

 but regarding it with attention one can see that this is due 

 to an immense number of black dots similar in size to the 

 pre-existing sporangia. These are the " zygospores " resulting 

 from the conjugation of gametes which have been produced. 

 Some varieties of Mucor, such as Mucor mucedo, produce 

 gametes rather infrequently, and from this we infer that the 

 growth-cycle is a long one and has to run through many 

 mycelia (finked together by the discontinuous spores) before 

 it ends with a gamete-forming mycelium. 



In the case of all moulds growth takes the form of a 

 mycelium, and this is simply a species of filament which in 

 growing gives off so many branches, and these so many others, 

 that it becomes an intricate network of filamentous tubes or 

 " hyphse." But in addition to the fact that there is no 



