DIDYMIUM 121 



D. squamulosum, as far as spores are concerned. A similar remark 

 may be made relative to the form of the columella which Rostafinski, 

 in his figures especially, would make diagnostic. The columella in 

 the sporangia with largest and roughest spores is that of a perfectly 

 normal D. squarnulosum. 



7. DiDYMiUM MELANOSPERMUM (Pers.) Macbr. 



Plate VII., Figs. 3, 3 a. 



1794. Physarum melanospermum Pers., Rom. N. Mag. Bot., p. 89. 

 1797. Didymium farinacemn Schrader, Nov. Gen. PL, p. 26, t. 5, Fig. 6. 



Sporangia gregarious, hemispheric, depressed, umbilicate below, 

 stipitate or sessile; the peridium firm, dull brown in color, frosted 

 with minute crystals of lime, breaking irregularly; stipe, when pres- 

 ent, short, stout, dull black, opaque, arising from a broad base or 

 hypothallus; columella large, prominent; dark-colored, rough above, 

 concave below; capillitium of more or less sinuous, usually dark- 

 colored threads, sparingly branched, and often with calyciform thick- 

 enings; spore-mass black, spores by transmitted light pale, purplish- 

 gray, spinulose or rough, 10-12 jx. 



A well-marked and common species, distinguished by its depressed 

 sporangium and dark-colored, opaque stipe. The latter is usually 

 very short, almost completely concealed in the concavity of the umbili- 

 cate sporangium. The columella is dark-colored, forming the floor 

 of the peridial cavity. 



Persoon first named this species as here. Later on, lister's Ann., 

 XV., 6, he substituted villosum as a more appropriate specific name. 

 Schrader rejects both names given by Persoon as unsuitable, and 

 suggests farinaceum. Schrad., op. cit., p. 27. 



New England, Ohio, Missouri, Alabama, Iowa, Nebraska; 

 Europe; probably cosmopolitan. 



8. Didymium minus Lister. 



Plate X., Figs. 4, 4 a, 4 h. 



1892. Didymium farinaceum Schr., var. minus, List, Mycetozoa, p. 97. 

 1896. Didymium minus List., Morg., Jour. Cin. Soc, p. 61. 

 1899. Didymium minus List., Macbr., A^. A. S., p. 89. 



