Dean—The Myxomycetes of Wisconsin. 
1245 
Didymium clavus (Alb. and Schwi,) Rabenhorst. 
1805. Physarum clavus Alb. and Seliw., Consp. Fung., p. 96. 
1844. Didymium clavus (Alb. and Schw.) Rabh., Ger t Cr. FI. 
no. 2282. ’ 
Macbride: 11 Sporangia gregarious, pale gray, discoid or pili- 
ate, depressed, stipitate; the peridinm dark-colored, frosted with 
calcareous crystals above, naked below; stipe short, slender, taper¬ 
ing upward, furrowed, arising from, a hypothallus more or less 
distinct, black; columella obsolete; capillitium of delicate threads, 
pale or colorless. little branched; spores violaceous, pale, nearly 
smooth, 6-8 «. ’’ Macbride adds that this species is well differen¬ 
tiated, easy of recognition by reason of its peculiar discoid spor¬ 
angia, calcareous above, naked and black beneath. He gives no 
figure of this form. 
Lister: “Sporangia scattered, disc-shaped, thick grayish white; 
sporangium wall thickened and brown at the base; capillitium 
profuse colorless or purple-brown threads; spores pale violet- 
brown, almost smooth, 5-8/x.” 
Massee finds sporangia plane below; some small ring-like dark- 
colored thickenings on the capillitium threads; spores smooth, 
dingy lilac, 6-8,a.” 
In my one small group of sporangia I find many differences 
from the above descriptions, yet enough correspondence to make 
it certain, in my opinion, that it is D. clavus. The hypothallus 
is not very evident but is noticeably black; the sporangia are dis¬ 
coid, not very much depressed; the stellate crystals are nearly alt 
asymmetrical, having one arm or ray longer than the others; the 
crystals are not as large and noticeable as Massee has pictured 
in his figures: the sporangia are markedly umbilicate both above 
and below» I do not find the base bare and dark, unless it is so 
up under the curve or umbilicus; the stipe I find as described; 
the capillitium is darker than the spores, purple-brown; I found 
some darker spots on the threads, but failed to see many of them 
and could not make them out to be rings, as seen by Massee; the 
spores in mine are quite uniformly 6/x, yet I found a considerable 
number to be 8/x in diameter. They are pale violaceous and 
nearly smooth, although I saw some which showed small spines. 
My one group was found growing on live moss at Blue Mounds, 
July 18, 1907. 
