FAMILY MYXOCOCCACEAE 



1043 



limiting membrane discernible, the spores 

 being imbedded in the slime holding the 

 mass together. Usually single, though 

 two or three fruiting bodies may become 

 joined to form an irregular mass; each is 

 attached to the substrate, however, and 

 never bud one from another. 



Spores: Spherical, with thick outer 

 wall or membrane. Highly refractile. 

 Stain very easily with any of the ordinary 

 bacterial or nuclear dyes. 2.0 microns 

 in diameter, seldom larger. 



Vegetative cells : Large, flexible, single. 

 Gram-negative rods with rounded ends. 

 No flagella, but move on surface of solid 

 or semi-solid substrate with a crawling 

 or creeping motion. Vary in size from 

 0.5 to 1.0 by 4 to 10 microns; average 

 0.75 by 5 microns. More or less distinct 

 cell wall often evident. 



Vegetative colony : Characteristics 

 vary with the substrate. 



On plain 1.5 per cent agar (no nu- 

 trients added) : Very thin and trans- 

 parent, often hardly visible except by 

 transmitted light. Little or no pig- 

 mentation. Surface covered with fine, 

 more or less regularly spaced ridges 

 causing a dull macroscopic appearance 

 without gloss or sheen. Margin very 

 thin and quite regular. 



On rabbit dung decoction agar: Col- 

 ony thicker, the surface being broken 

 by veins or ridges radiating from the 

 center. Thick central area often smooth 

 and glossy while margin much the same 

 as that on plain agar. Veins or ridges 

 extend outward from center in loose 

 spiral, always in clock-wise direction. 

 Pigmentation, yellow to pale orange, 

 confined to thicker central portion, 

 extends part way along veins to margin. 



On nutrient agar: Growth poor. Col- 

 ony thick, at first heavily veined, the 

 veins later merging to form an irregular 

 glossy surface. Colony remains small, 

 pigmentation usually fairly heavy; mar- 

 gin thick, irregular to lobate. 



Physiology : Grows well on mineral 



salt-agar to which has been added dul- 

 citol, inulin, cellulose, reprecipitated 

 cellulose or starch; hydrolyzes starch; 

 does not destroy cellulose to any appreci- 

 able extent. Best growth on suspension 

 of killed bacterial cells in agar ; suspended 

 cells in growth area lysed. Develop- 

 ment completelj^ inhibited by arabinose, 

 largely by maltose and mannose. 



Source : Isolated from dried cow dung, 

 Ames, Iowa. 



Habitat : Decomposed bacterial cells 

 in dung. 



Illustrations: Beebe {loc. cit.) Figs. 

 1-28. 



5. Myxococcus stipitatus Thaxter. 



(Bot. Gaz., 23, 1897, 395.) 



Etjniiology : From Latin stipes, stalk; 

 stalked. 



Swarm stage (pseudoplasmodium): 

 Rods 0.5 to 0.7 by 2 to 7 microns or 

 longer. Grows well on nutrient agar, 

 but does not fruit readily. 



Fruiting body: Spore mass nearly 

 spherical, 175 microns in diameter, del- 

 iquescent, sessile on a well developed 

 compact stalk, white to yellowish and 

 flesh color. Spores 0.8 to 1.2 by 1.0 to 

 1.15 microns. Stalk 100 to 200 microns 

 long, 30 to 50 microns wide. 



Source and habitat : Thaxter {loc. cit.), 

 repeatedly on dung in laboratory cul- 

 tures at Cambridge, Mass., Maine, Ten- 

 nessee. Krzemieniewski (1927, loc. cit.), 

 common in Polish soils. 



Illustrations: Thaxter {loc. cit.) PI. 

 31, Figs. 30 to 33. Krzemieniewski, 

 Acta Soc. Bot. Poloniae, 4, 1926, PI. II, 

 Figs. 13-14. 



6. Myxococcus ovalisporus Krzemien- 

 iewski. (ActaSoc. Bot., Pol. ,4, 1926,15.) 



Etymology : ^Modern Latin ovalis, oval , 

 Greek sporos, seed. Oval spored. 



Swarm stage (pseudoplasmodium): 

 Not described. 



Fruiting bodies : Produces almost spher- 

 ical, characteristically shortened, ovoid 



