254 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



The ]\Iycetozoa (Myxogastrales, Acrasiales, Labyrinthulales, and Plasmodio- 

 phorales) are, following De Bary, placed outside the vegetable kingdom, being 

 considered as derived from Protozoa of the group Rhizopoda and not progress- 

 ing further to produce recognized fungus groups. When the flagella of the 

 motile cells have been examined, they are found to occur in pairs, both of the 

 whiplash type, thus barring any connection of tlie Plasmodiophorales with the 

 Olpidiopsidaceae, where one of the flagella is of the tinsel- type and the other of 

 the whiplash type. The true fungi are believed to begin with the Phycomycetes. 

 The simplest of these fall into three series : Chytridiales, with a single posterior, 

 whiplash type flagellum; Hyphochytriales, with a single anterior flagellum of 

 the tinsel type; and Lagenidiales (including Woroninaceae and Olpidiopsidaceae, 

 but not the Plasmodiophoraceae) with two anterior or lateral flagella, one of 

 the tinsel type, the other of the whiplash type. The Chytridiales connect di- 

 rectly with the Blastocladiales and Monoblepharidales, this line then ending 

 blind; the Hyphochytriales have no recognized further development; the Lage- 

 nidiales lead onward to the Saprolegniales and Peronosporales. Two paths of 

 evolution of the Chytridiales, Hyphochytriales, and of the simpler Lagenidiales 

 are suggested. They may be primitively simple, derived from some algal ances- 

 tors of the group of Heterokostae, in which the flagella are of the two types. By 

 the loss of the tinsel type flagellum the Chytrid type may have originated; by 

 loss of the whiplash flagellum the Hyphochytrial group might have developed; 

 while the Lagenidiales line may have had its beginning with the retention of 

 both types of flagellum. But, contrariwise, these simple forms may have arisen 

 by simplification from some fungi of the Lagenidiales, Saprolegniales, Perono- 

 sporales lines which, as suggested by De Bary, Sachs, Gaumann, and others 

 may have arisen from algae in the vicinity of Vaucheria. 



The author seeks the origin of the Mucorales in the soil-inhabiting Sapro- 

 legniales in which the sporangia produce encysted spores (as in Ai^lanes) in- 

 stead of the zoospores usually found in that order. The approximately equal 

 gametangia, such as unite to form the zygospore in Mucor may be a much de- 

 rived form, for there are a number of genera in the Mucorales (e.g., Dicrano- 

 phora and ZygorJiynchus) in which the two uniting gametangia are very unequal 

 in size and appearance, more like the antherid and oogone in some of the Sapro- 

 legniales. Akin to the Mucorales are probably the Entomophthorales and the 

 Zoopagales. In the author's opinion, the Phycomycete line comes to an end there, 

 not proceeding to the higher fungi. 



The Ascomycetes are believed to have arisen from some algal ancestor re- 

 lated to the Florideae. In this algal group the oogone (carpogone) consists of 

 a swollen basal portion with a receptive trichogyne to which a naked sperma- 

 tium adheres. From the basal portion then grow out hyphae, at whose extremi- 

 ties are produced the carpospores or, in Liagora tctrasporifcra, tetrasporangia. 

 This structure of carpogone, threads, and spores is a spore-fruit wdth, usually, 

 surrounding and protecting vegetative cells. In many of the Ascomycetes occur 



2. The terms tinsel flagellum and whiplash flagellum were used by Couch (1941) in 

 the sense that Vlk (1938) used the words Flimmergeissel and Peitschengeissel. They 

 designate respectively the more slender, wavy flagellum with numerous fine lateral threads 

 and the thicker, stiffer flagellum of two parts — a thick basal portion and, at its upper end, 

 a thin lash. These fine details can be observed only by special staining methods or by 

 observation with the dark-field microscope. 



