228 INTRODUCTION TO THE STUDY OF FUNGI 



order, which includes the old typical Mucors and their 

 allies — almost the sum total of the Physomycetes of former 

 times ; and also the Peronosporeae, or rotting moulds, previously 

 classed with the Hyphomycetes ; as well as the " white rusts " 

 (Cystopi), formerly united with Uredines. In addition to these 

 are the fish moulds, or Saprolegniaceae ; and the insect moulds, 

 or Untomophthoraceae ; so that altogether there are four very 

 distinct families, with well-developed hyphae ; to which must 

 be added two other, inferior, groups, in which the hyphae are 

 obsolete, for, a long time regarded as outside families, with 

 obscure affinities, but remotely associated with the Uredines 

 under the names of Chytridium, Synchytrium, and Protomyces. 

 This association of apparently rather heterogeneous elements 

 is held together by the conservating bond of a dimorphic 

 reproduction ; otherwise their relationship is, at first sight, so 

 obscure that it will be necessary to advert to each family 

 separately. 



It has already been intimated that four of the families 

 possess a conspicuous vegetative system, in a unicellular 

 creeping mycelium, giving rise to erect, simple, or branched 

 threads, which bear the conidia, or otherwise asexual repro- 

 ductive organs. Although agreeing in this, the organs them- 

 selves differ considerably in the four families, inasmuch as the 

 Mucoraceae develop cysts, or bladder-like cells (sporangia), 

 which enclose either many or only one reproductive cell, or 

 gonidium. These cysts are terminal on the fertile hyphae, 

 and may be produced singly or in clusters. In the Perono- 

 sporaceae there are no true cysts, but naked gonidia, which 

 may be passive, and germinate directly, or their contents may 

 become differentiated into zoospores, or zoogonidia ; that is to 

 say, active ciliated zoospores, which at length become passive 

 and germinate. The Saprolegniaceae are aquatic, and produce 

 zoospores within the changed hyphae ; and the Untomoph- 

 thoraceae are parasitic on insects, and develop single conidia 

 on short sporophores. Thus it will be seen that there are 

 distinct features in the asexual reproduction of the four 

 families sufficient for their discrimination. It may be added, 

 as a further distinction, that the Mucoraceae are saprophytic 

 on dead animal or vegetable substances. The Peronosporaceae 



