10 THE LOWER FUNGI— PHYCOMYCETES 



have been regarded by van Tieghem, de Bary, Zopf, Harper, 

 Olive, and others as belonging near the Myxomycetes, and are 

 here so treated, though the differences between the two groups 

 are at least as pronounced as their points of similarity. 



In the Acrasieae the organism exists during the vegetative 

 phase in the form of naked amoeboid cells (myxamoebae). 

 These never pass into the ciliate swarmspore condition which, 

 at certain periods, characterizes the motile cells of the Myxo- 

 mycetes. They crawl about over the substratum, ingesting and 

 feeding on solid materials, and increase greatly in number by 

 repeated divisions. At the close of the vegetative period under 

 the influence of some unexplained impulse, they move toward 

 common centers and collect into definite colonies which have been 

 termed by some writers pseudoplasmodia or aggregation-plas- 

 modia. The myxamoebae composing these colonies do not 

 fuse. Each cell retains its individuality throughout the further 

 development of the colony and the subsequent formation of 

 the mature fructification. The myxamoebae crawl over one 

 another and become heaped up to form sessile or stalked masses 

 of definite form, which in some species exhibit considerable com- 

 plexity. Each cell then usually assumes a cellulose wall and 

 becomes a spore. In two genera {Sappinia, Guttulinopsis) a 

 wall is not formed, but the peripheral protoplasm is hardened 

 into a protective layer. The cell in such cases is called a pseudo- 

 spore. These spores or pseudospores lie in a definite mass, 

 being held together by a mucous substance, and constitute the 

 fructification. These masses have a superficial resemblance to 

 the colonies of bacterial cells formed in the Myxobacteriaceae. 

 At the close of a period of rest the spores germinate by cracking 

 open, and the content of each escapes as a vegetative myxamoeba. 

 The pseudospores pass into the vegetative phase gradually with- 

 out casting off a membrane of any sort. Under unfavorable 

 environmental conditions myxamoebae may enter the resting 

 condition isolated from one another as microcysts. 



Though the Acrasieae resemble the Myxomycetes in possessing 

 a naked amoeboid phase, their vegetative period includes 

 neither the swarmspores nor the true plasmodium of that group. 

 Moreover, there is no condition which shows any resemblance to 

 the net-plasmodium of the Labyrinthuleae. In the Acrasieae 

 the vegetative stage ends when formation of the pseudoplas- 

 modium begins. The latter is, therefore, a structure connected 



