ioo INTRODUCTION TO THE STUDY OF FUNGI 



yards if the conditions are favourable, and can only rarely be 

 traced to the production of any reproductive apparatus, such 

 as pileus and hymenium. It has been demonstrated that one 

 form of Phizomorpha may be traced to a development in 

 Agaricus melleus, another form in the common Polyporus 

 squamosus, and yet another in Fom.es annosus. 



The mycelium is also remarkably in evidence in the large 

 order Hyphomycetes, or moulds, in which there is always at 

 first a creeping mycelium of entangled threads, from which 

 arise afterwards the erect and sometimes branched conidio- 

 phores or fertile threads, surmounted by conidia or spores. 

 Instances will occur in which, owing to a superabundance of 

 moisture, no fertile threads are produced and the whole Fungus 

 consists of a mass of sterile mycelium. It is only necessary to 

 refer to one of the forms of " blue mould," named Penicillium 

 crustaceum, which will produce a profuse mycelium in fluids, 

 forming an expanded felted mass resembling the substance 

 known as the " vinegar plant." So long as there is a plentiful 

 supply of liquid the vegetative system will go on indefinitely, 

 but a check must take place and the supply of moisture be cut 

 off before erect fertile threads and spores will be developed. 

 Not only the saprophytic but also the epiphytic moulds 

 commence with a mycelium, in the latter instance concealed 

 within the substance of the host-plant. Thus we have 

 characteristic examples in the genus Pamularia amongst 

 the Mucedineae, and in Cercospora amongst the Dematieae. 

 These have their analogues in the Peronosporaceae, formerly 

 classed with Mucedines, but now associated with Mucoraceae as 

 Zygomycetes. 



The majority of the genera of the Physomyeeteae are on an 

 equality with the Hyphomyeetes in the strong development of 

 the mycelium ; and it is in connection with this mycelium that 

 the phenomenon of conjugation takes place which results in 

 the production of zygospores, or resting spores, by means of 

 which the species are preserved through the winter. This 

 takes place not only in the Mucoraceae, which are mostly 

 saprophytes, but also in the Peronosporaceae, which are destruc- 

 tive epiphytes. In the former the mycelium is more or less 

 superficial, and in the latter innate. 



