250 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



IV. Carposporeae. Sexual reproduction results in the production of a spore fruit 

 With chlorojihyll Lacking chlorophyll 



Coleochaeteae Ascomycetes (including the Lichens) 



Florideae Aecidiomycetes 



Characeae Basidiomycetes 



Sachs believed that the Saprolegniales and thence the Peronosporales arose 

 from algae closely related to Vaucheria with a few differences : disappearance of 

 chlorophyll, lack of free-swimming male gametes (these being replaced by a con- 

 jugation tube from the antherid piercing to the egg), and the production of 

 numerous simple biflagellate zoospores instead of a large compound zoospore 

 with hundreds of pairs of flagella. The branched coenocytic vegetative struc- 

 ture with cellulose cell walls, the production of zoospores in terminal segments 

 of the hyphae, and the formation of large oogones with antherids usually aris- 

 ing nearby are characters common to Vaucheria and the Saprolegniales. 



The idea that Mucorales represent developments from the Conjugatae in 

 which the chlorophyll has been lost was adopted by Sachs from Brefeld, who 

 emphasized the similarity of the formation of the zygospores in both groups 

 of organisms. Although the suggestion of De Bary and Sachs that the Sapro- 

 legniales are probably derived from Vaucheria-like algae has persisted in some 

 quarters (Gaumann, 1949), mycologists have been led to reject the idea of the 

 close relationship of these groups because of other factors: the type of hyphae 

 tubular coenocytic in Mucorales, cellular with uninucleate cells, in Conjugatae; 

 cell wall mainly of chitin in the former, of cellulose in the latter; and abundant 

 production of asexual wind-borne spores in the former, no special asexual cells 

 in the latter. 



In the fourth class, Carposporeae, the central feature is the production of a 

 spore fruit, i.e., a mass of cells some of which are the spores which will produce 

 the new plant. The spore fruit in the Ascomycetes, in which sexual organs are 

 still functional, gives rise to ascospores contained in asci, at the ends of ascog- 

 enous hyphae originating from fertilized oogones. Around these hyphae may 

 also be present the vegetative hyphae that form the paraphyses and the main 

 body of the perithecium or apothecium. In many of these Ascomycetes are pro- 

 duced nonmotile spermatia which unite with the receptive threads (tricho- 

 gynes) from the oogones and thus bring about the fertilization. This is similar 

 to what happens in the Florideae and gave rise to Sachs's suggestion of the origin 

 of the Ascomycetes from that group. This view still persists among many my- 

 cologists (see Vuillemin, 1912, in which a very full discussion is given of the 

 various suggested systems of classification of the fungi). 



Brefeld did not accept the ideas of Sachs and rejected those of De Bary, 

 except the origin of the Oomycetes from the Siphoneae. For him, this group 

 does not represent true fungi. The true fungi begin with the Mucorales, which 

 he considers to have developed from algae that produced zygospores (e.g., Con- 

 jugatae). He emphasizes that the algae retained their sexuality and evolved into 

 the higher green plants. The primitive fungi (the Mucorales) quickly began to 

 magnify the importance and complexity of their asexual reproduction at the 

 expense of the sexual reproduction, which soon disappears as evolution pro- 

 gresses toward the higher fungi. In the main line of fungus evolution, the basic 

 group is class Zygomycetes (the class Oomycetes, in his view, comes to a blind 



