Physarum 29 



Distribution: Common and abundant throughout conti- 

 nental North America 



Illustration: Lister. Mycetozoa ed. 3. pi. 14. 



This species forms large and many developments of sporangia 

 at one time. I have seen, in the swamps, sporangia covering the 

 stalks of living ferns for several hundred square feet, and dozens 

 of covered logs in the forests. Two varieties, known from Europe 

 and elsewhere, var. dictyospora and var. glohosa, have not yet been 

 found in North America. The type of Didymium Ciirtisii Berk., 

 from South Carolina, differs from typical B. ruhiginosa only in 

 being sessile or shortly stalked, as Lister says, and a specimen col- 

 lected by Prof. Thaxter (N. Y. B. G. no. 10711) at Eustis, Florida, 

 is similar, and almost limeless. The type of Craterium ohovatum 

 Peck is typical B. ruhiginosa. Lister has examined the type of 

 B. subaqiiila Macbr. from Maine, and regards it as a sessile form 

 of B. ruhiginosa similar to D. Ciirtisii Berk. 



Genus 3. PHYSARUM Persoon, Neues Mag. Bot. 1: 88. 

 1794. 



Sporangia stalked, sessile, or forming plasmodiocarps; sporan- 

 gial wall either single, or consisting of two more or less separable 

 layers, with deposits of minute, rounded lime-granules distributed 

 in loose or dense clusters, or compacted into a crust. Stalk 

 membranous, tubular (except in P. penetrate, in which the stalk 

 is solid and translucent), wrinkled with longitudinal folds, either 

 translucent, or opaque with deposits of lime or refuse matter in 

 the wall-substance or in the cavity of the tube. Capillitium 

 forming a network of hyaline threads with vesicular expansions 

 containing calcareous deposits (lime-knots), occasionally without 

 such deposits in weak forms. 



Type species: Physarum aureum Pers. 



Sporangia stalked (occasional sessile forms). 

 Stalks charged with lime throughout. 

 Capillitium lax. 



Stalk white; sporangia white or gray; lime- 

 knots large, white; columella none. \. P. leucopus 

 Stalk white, rarely yellow or rufous; sporan- 

 gia tawny or yellow; columella conical. 2. P. melleum 

 Stalk white or yellow; sporangia sulphur- 

 yellow or olive-yellow; columella none. 3. P. sulphuretim 

 Capillitium dense, persistent. 



Stalk, sporangium and lime-knots j'ellow, 

 pale yellow or orange. 



