300 RESEARCHES ON FUNGI 



In the Myxobacteriaceae, e.g. Chondromyces crocatus, the individual 

 bacteria by mass action build up an aerial gelatinous branched stalk 

 or cystophore which ultimately bears cysts in which are packed living 

 bacteria. Social organisation is exhibited by the bacteria in two ways : 

 (1) in the common effort involved in the construction of a complex 

 fructification, and (2) in that the bacteria which are enclosed in the 

 stalk are sacrificed for the welfare of the bacteria enclosed in the cysts, 

 which alone are able to reproduce the species. 



In the Acrasieae, e.g. Dictyostelium mvcoroides, the myxamoebae 

 form an aggregate plasmodium in which the individuals retain their 

 identity. Finally, a plasmodium builds up a long, sterile stalk crowned 

 by a globular mass of naked spores. The myxamoebae which form the 

 stalk never take a direct part in reproduction, but they assist reproduc- 

 tion by constructing an apparatus (the stalk) up which the spore- 

 forming myxamoebae may ascend to take up a position which presumably 

 is favourable for spore- dispersal. 



In the Mycetozoa, social organisation is exhibited : (1) by the union 

 of young Plasmodia to form a larger compound plasmodium which acts 

 as a whole in the formation of sporangia ; (2) by zygotes, when beginning 

 to feed, ingesting unpaired amoebulae and using them as food ; and 

 (3), as in Arcyria pomiformis, by the spores being differentiated into 

 two kinds — the spores proper which reproduce the species, and the 

 spore-like cells which are never disseminated but fill the stalk and 

 mechanically strengthen the apparatus in which the true spores are 

 developed and from which they are dispersed. 



In most of the Phycomycetes, e.g. Mucor, Pilobolus, and Saprolegnia, 

 apart from the requirements of sex, the individual mycelia of any species 

 do not fuse together and do not display any social organisation. 



In the Hymenomycetes — the leading group of the Higher Fungi — 

 both in homothallic and in heterothallic species, any two mycelia, what- 

 ever their sexual phase, on coming into contact with one another fuse 

 together hyphally, so that, in dung-balls, wood, leaves, and other 

 substrata, many mycelia of one and the same species often combine to 

 form a compound mycelium which is a three-dimensional network of 

 hyphae. Such a compound mycelium acts as a unit in producing 

 fruit-bodies. 



Social organisation in the Hymenomycetes has been illustrated with 

 special reference to Coprinus sterquilinus. A fruit-body of a Coprinus, 

 as Brefeld has shown, owes its origin to a single cell of the myceHum. 

 Where, therefore, as in Coprinus sterquilinus, say one hundred mycelia 

 in a dung-ball have combined together to form a single compound 

 mycelium which produces one large fruit-body, the fruit-body, genetically, 

 is the product of one of the components of the compound myceHum but, 

 nutritionaUy, is developed at the expense of all of the one hundred 

 components : one of the components succeeds in reproducing itself, 



