94 COMPARATIVE MORPHOLOGY OF FUNGI 



forms, which approximately correspond to Cladophora and the isogamous 

 Siphonales. As intermediate forms are wholly lacking and apparently 

 the morphological significance of simple structures like the Mucoraceous 

 sporangium are still unknown, phylogenetic speculation is unfruitful. 

 The present tendency is rather to connect the Zygomycetes with the 

 Chytridiaceae or the more primitive Oomycetes. In the Chytridiaceae, 

 the comparison of Polyphagus with Conidiobolus is suggestive, as is in 

 the Oomycetes, a comparison with the Ancylistaceae, in which one needs 

 only to imagine the absence of the conjugation tube in order to obtain 

 a picture of a somewhat heterogamous zygogamy. It is quite probable 

 that the Zygomycetes include phylogenetically heterogeneous organisms, 

 which are only similar in the isogamous copulation of their coenocytic 

 gametangia. 



In their classification, the Zygomycetes fall into two series, one of 

 which forms sporangia, the other conidia. The sporangial series includes 

 the Mucoraceae and the Endogonaceae, whose difference lies in the degree 

 of development of their fructifications. The conidial series includes 

 the Entomophthoraceae. 



Mucoraceae. — This family is mostly saprophytic on plant or animal 

 remains, more rarely parasitic on other Mucoraceae or on higher plants 

 and animals. Some forms, e.g., Mucor racemosus and M. mucedo, may 

 be regularly isolated from the air, others appear in the earth and form 

 there in definite soils and definite associations. They are found in damp 

 ground in coniferous forests, in Norway the principal species being M . 

 Rammannianus , M strictus, M. flavus and M. sylvaticus. In cultivated 

 ground occur M. mucedo, M. sphaerosporus, M. racemosus, etc. They 

 play there a large part in the decay of organic substances (Hagem, 1907, 

 1910). A few species, because of special enzymes (e.g., alcoholic fer- 

 mentations by M . javanicus, or starch hydrolysis by Rhizopus Oryzae, 

 have attained great technical importance (Wehmer, 1907). Still others, 

 as M. pusillus and Absidia Lichtheimi (M. corymbifer) , are important in 

 medicine as they cause dangerous mycoses of internal organs. 



The thallus corresponds entirely to that of the Oomycetes. It 

 consists of ramose, coenocytic hyphae without septa; in old age and in 

 the development of fructification, septa are formed irregularly to cut off 

 the older vacuolate sections from the younger. An exception is Haplo- 

 sporangium, whose hyphae early divide into numerous shorter or longer 

 segments (Fig. 65). Furthermore, the hyphae of some genera in sugar 

 solutions and anaerobic conditions break up into oidia (Fig. 54, 9) which 

 develop further by sprouting; this sprout mycelium (Fig. 54, 4, 6 and 7), 

 has ability to ferment in common with true yeasts. In Mortierella 

 and Syncephalis, the hyphal branches fuse where they come in contact 

 so that the mycelium frequently attains a reticlulate appearance. Hetero- 

 thallic species generally have no definite sexual dimorphism, the strains 



