ACRASIALES 41 



this reason he gave slime molds the name Mycetozoa and placed 

 them outside the plant kingdom. Meantime Cienkowski (1863, 

 1863a) turned his attention to this group, and as an outcome of 

 his studies, together with those of de Bary, thoroughly estab- 

 lished the fact that spores of slime molds germinate by the for- 

 mation of swarm cells, that these swarm cells fuse to initiate the 

 Plasmodium (apparently this term was first employed by Cien- 

 kowski), and that the plasmodium eventually ceases to grow 

 and becomes transformed into the fructification. 



A series of taxonomic treatises on this group have appeared, 

 beginning with that of Rostafinski (1873), a pupil of de Bary. 

 His studies are the basis of present-day classification. Then fol- 

 lowed the classification of Massee (1892) and the monograph of 

 Lister (1894), which has undergone two revisions by his daugh- 

 ter. Meanwhile a treatise by Macbride (1899) of the North 

 American slime molds appeared and was completely revised in 

 1934 [Macbride and Martin (1934)]. In the present account 

 the Myxomycetes are regarded as including the three orders, 

 Acrasiales, Labyrinthulales, and Plasmodiophorales, that are out- 

 side the subclass of true slime molds, Myxogastres. This is done 

 arbitrarily and not on the basis of evidence of relationship to the 

 Myxobacteriales, the flagellate Protozoa, or the Myxochytridiales. 



Acrasiales. The Acrasiales comprise a group of approxi- 

 mately 20 species that occur on dung and on decaying leaves and 

 wood. There is reason to beheve that they are of general oc- 

 currence in soils containing organic matter of any sort. They 

 are characterized by abrupt separation into vegetative and fruit- 

 ing stages. On germination their spores produce naked amoe- 

 boid cells, called myxamoebae. Each cell is uninucleate and, in 

 the presence of available food (bacteria), is capable of giving 

 rise to an indefinite number of cells like itself. Dictyostelhim dis- 

 coideum, as observed by Raper (1940), typifies the developmental 

 structure of this order. He found that each amoeboid cell re- 

 mains a distinct entity and that the cells aggregate, without 

 fusing, to constitute the pseudoplasmodium. That they are all 

 separate may be shown, as Raper demonstrated, by placing a 

 pseudoplasmodium in water. As growth proceeds, the pseudo- 

 plasmodium becomes a cylindrical body that migrates as a unit 

 throughout the substratum or over its surface. Eventually it 

 becomes transformed into a fruiting structure, a sporocarp, con- 



