ORDER MYXOGASTRALES OR SLIME MOLDS 



23 



considered. The ordinal limits as here treated are far wider than those 

 found in the monographs of the Slime Molds by Lister (1925), or Macbride 

 and Martin (1934), and others. These four orders may be included in the 

 Subclass Mycetozoa of Class Sarcodina, Phylum Protozoa. The four 

 orders are Myxogast rales, the true Slime IMolds, Acrasiales, Plasmo- 

 diophorales and Labyrinthulales. There are other organisms probably 

 closely related to these that have been studied by zoologists but which 

 have usually been neglected by botanists and are not considered here. 



Order Myxogastrales or Slime Molds. Often called Myxomycetes or 

 Myxogastres, the Myxogastrales or Slime Molds compose the most 

 numerous group of this subclass. They are terrestial organisms or inhabi- 

 tants of manure, decaying wood, decaying fungi, etc. Their spores are 

 produced upon or within aerial sporangia and are more or less dependent 

 upon wind for their distribution. In general the life history (with some 

 modifications) is as follows: The spore, upon absorbing water, cracks open 

 its cell wall and escapes as a single (in some species by division of the 

 nucleus before germination, two) naked uninucleate swarm spore or 

 planocyte, rounded posteriorly and tapering to the anterior end from 

 which arises a single flagellum or in many cases two flagella. De Bary 

 (1859) described and figured occasional biflagellate zoospores of Fuligo 



Fig. 1. Myxogastrales. (A-H) Physarum polycephalum Schw, (A) Spore. (B) Ger- 

 minating spore. (C, D) Swarm spores. (E) Uniting swarm spores. (F, G) Amoeboid 

 zygotes. (H) Portion of Plasmodium. (I-J) Physarella oblonga (B. & C.) Morg. (I) 

 Uniflagellate swarm spore. (J) Biflagellate swarm spore. (All figures much mag- 

 nified.) (A-H, after Howard: Am. J. Botany, 18(2). I-J, after Sinoto and Yuasa: The 

 Botanical Magazine [Tokyo], 48(574) :722.) 



