BESSEY: MYCOLOGY 247 



have been the more primitive forms and by what routes evolution may have pro- 

 duced the different groups. Theoretically, now, the ideal system of classification 

 will attempt to indicate these lines of descent (or shall we say, ascent) from 

 the first organisms that we may call fungi. Since, however, fungi are not easily 

 preserved as fossils, we cannot call upon the phytopaleontologists to assist us 

 by showing what types of fungi occurred at each geological era. Therefore 

 we have to depend upon the study of the ends of the twigs of the phylogenetic 

 tree and by comparing these to surmise what the trunk and the main evolu- 

 tionary branches probably were. 



Because of the structural differences in different groups of fungi and the 

 different chemical constitution of their cell walls, as well as differences in their 

 life histories, some of the earlier mycologists who believed in evolution concluded 

 that the fungi are not necessarily a single phylctic series but that evolution from 

 algae to fungi may have occurred at several different points. The necessary 

 consequence of the acceptance of such a hypothesis would be belief in the poly- 

 phyletic nature of the fungi we are acquainted with, in other words, these would 

 not represent a great group of common descent. The different groups, arising 

 from different algae, would not be interrelated, except as one traces relation- 

 ship down through their various ancestral algal stocks to their common algal 

 ancestor. 



Some of the suggested alga-to-fungus relationships are as follows : origin of 

 Chytridiales (in the wide, older use of this term) from unicellular algae, taking 

 into consideration the existence of certain somewhat intermediate genera which 

 are still considered as algae but which live endophytically, e.g., Chlorochytrium, 

 Endosphaera, RJwdochytrium, etc. On the contrary, it has been suggested that 

 the Chytridiales are descended l)y simplification from Saprolegniales. Another 

 suggested relationship is Vaucheria-Uke algae to Saprolegniaceae, taking into 

 consideration the occurrence of the endophytic genus Phyllosiphon, showing 

 that such an intermediate step may occur in this area of relationship. From 

 the Saprolegniales would have arisen the Peronosporales and possibly, by sim- 

 plification, the Chytridiales. The suggested origin of Monohlepkaris from Oedo- 

 goniuyn is certainly erroneous, now that the structures and life histories of both 

 have been more fully elucidated. Similarly, the supposed connection of Mucor 

 and Spirogyra cannot be upheld. One hypothetical connection, Florideae to As- 

 comycetes, suggested by Sachs (1874), has so many data to support it that to 

 this day many mycologists, including the writer, are inclined to accept the 

 hypothesis (see Bessey, 1942). 



The classifications of the pre-evolution days have undergone great modifica- 

 tions, Fries (1821-1832) divided the fungi into four classes. 



1. Coniomycetes: sporidia naked, without receptacles. Four orders, all except part 

 of order Entophytae corresponding to our present Fungi Imperfecti. This latter order 

 contained also the rusts and smuts. They were not true organisms, according to Fries, but 

 exanthemata of diseased plants. 



2. Hyphomycetes: thallus floccose, the sporidia borne upon or among the hyphae. 

 These, too, were mainly Fungi Imperfecti. 



3. Gasteromycetes: the whole fungus closed, containing the sporidia in its interior. 

 This includes the present-day Gasteromycetes, the Mucorales, the Mycetozoa, and the 

 Pyrenomycetes. 



4. Hymenomycetes: hymenium soon exposed, bearing the sporidia superficially, in the 



