PHYSARUM 71 



the lime-knots angular or rounded, white, connected by hyaline 

 threads; spores in mass black, by transmitted light dark violet, densely 

 spinulose, 12-15 //. Plasmodium watery white or gray. 



A very variable species in many particulars. The sporangia in the 

 same cluster are stipitate and sessile, ovoid and spherical. Our descrip- 

 tion does not quite agree with that of Rostafinski; it is the outer 

 peridium that is with us white, burdened with lime; the inner is simpler 

 and comparatively thin. The whiteness of the outer peridium is, how- 

 ever, easily displaced. The colony may not show it at all, in which case 

 the peridia remaining give to the entire fructification a pale lead color, 

 very characteristic. The disposition of the lime in the capillitium is 

 also notably variable. Specimens occur which suggest Rostafinski's 

 Crateriachea; that is, the lime is massed as a snow-white pseudo- 

 columella in the center of each sporangium. In such cases the lime of 

 the outer peridium may be scanty or limited in amount, not forming a 

 calcareous cap. The size of the spores is also variable. Rostafinski 

 gives 12.5-14.2 n; not infrequently a single spore reaches 16 n, a very 

 unusual range of variation. 



The species is fairly common in the upper Mississippi valley, and 

 can be obtained in quantity where once it appears, as the plasmodia 

 are profuse. 



Physarum lividum Rost. (Mon. 95) is but a less calcareous form of 

 this, as is evident even by the author's description. Professor Morgan 

 thought P. lividum a phase of P. griseum Lk. Link, however, reckons 

 P. griseum the same as P. cinereum. 



Forms without a stipe, with thinner sporangium wall and with 

 spores paler and smoother on one side are segregated as the var. lividum 

 Lister in the English monograph. 



Eastern North America to Kansas, Washington, Nicaragua. Es- 

 pecially to be looked for on the bark of fallen stems of Populus and 

 Negundo. Also South America; Europe, Asia, Africa. 



43. Physarum mutabile (Rost.) Lister 



Mycetozoaed. 2. 53. 1911. 



1875. Crateriachea mutabilis Rost., Mon. 126. 



1894. Physarum cinereum (Batsch) Pers. ex List., Mycetozoa 55, in part. 



1895. Physarum crateriachea List., Jour. Bot. 33 : 324. 



Sporangia ovoid, cylindrical or subglobose, 0.4-0.6 mm. in diameter, 

 stalked or sessile, sometimes plasmodiocarpous, white, becoming 

 yellowish gray with the disappearance of the peridium, sessile or 

 stipitate, stipes when present yellow, with or without lime, often con- 



