Physarum 57 



Var. leucophaeum (Fries) Lister, Mycetozoa 51. 1894. 



•Physarum leucophaeum Fries, Sj^mb. Gast. 24. 1818; Macbr. & Martin, 

 Myxomycetes 77. 1934. 



Sporangia erect, 0.5 to 1 iiini. diain., stalked, sessile or forming 

 plasmodiocarps; stalks stouter; columella none, or occasionally 

 present as an irregular or conical continuation of the stalk; 

 capillitium with larger and often branching lime-knots; spores 

 9-11 IX diam. 



Var. robustum Lister, Mycetozoa 51. 1894. 



Sporangia erect, often forming plasmodiocarps; stalks gray or 

 white from enclosed lime; capillitium more rigid with the central 

 lime-knots often confluent to form a pseudo-columella. 



Type locality: Europe. 



Habitat: On dead wood. 



Distribution: Common throughout North America. 



Illustrations: Lister, Mycetozoa ed. 3. pi. 37, 38. 



The typical form is quite distinct and easily recognized. It 

 is connected with P. viride through var. incanum of that species 

 which may be almost white except for pale yellow lime-knots. 

 On the other side, P. nutans merges gradually into P. notabile 

 through a long line of intermediate forms, some of which have 

 been regarded as species at other times. The Listers have set out 

 vars. leucophaeum and robustum as centers approaching P. nutans, 

 and the arrangement is probably best for this series of confusing 

 forms. The treatment by Macbride & Martin in the Myxomy- 

 cetes is illogical. They recognize P. leucophaeum as a distinct 

 species, and then apply var. robustum as a variety of P. nutans, 

 although it is a more robust form and clearly intermediate between 

 var. leucophaeum and P. notabile. Both varieties form sessile 

 sporangia and plasmodiocarps which are not present in normal 

 developments of the typical form. The spores of P. nutans and 

 its varieties are usually smaller and paler than those of P. notabile, 

 but there are colonies of the latter which have paler or smaller 

 spores. The spores should be studied in mass as well as by trans- 

 mitted light. There are many collections which cannot be placed 

 definitely, although a knowledge of the field conditions will help, 

 sometimes, to determine them. The species and its varieties 

 produce small developments. 



