dictydium] heterodermaceae 185 



Genus 28.— DICTYDIUM SchraderNov. Gen. PL, 11 (1779). 

 Sporangia globose, stalked ; sporangium-wall formed of 

 parallel ribs extending from the base nearly to the apex, 

 connected by slender transverse threads, the intervening 

 wall evanescent or persistent only as a shallow cup. 



1. D. cancel latum Macbr. N. Am. Slime-Moulds, 172 

 (1899). Plasmodium purple-black. Total height 1 to 2 mm. 

 Sporangia gregarious, globose, usually cernuous, 05 to 

 0*7 mm. diam., dark red-brown, rarely purple ; sporan- 

 gium-wall forming a net with nearly square meshes, composed 

 of numerous (40 to 50) rigid longitudinal ribs 5 fx thick, con- 

 nected by slender transverse threads, and often forming an 

 irregular net at the apex ; basal cup scarcely developed. 

 Stalk subulate, bent or twisted at the slender apex, rich 

 purple-brown, one to three times the height of the sporan- 

 gium. Spores pale red, minutely warted, 4 to 7 /a diam., 

 usually with two to four purple plasmodic granules on the 

 spore wall. — Mucor cancellatus Batsch Elench. Fung., ii. 135, 

 fig. 232 a, b, c (1789). Stemonitis cancellata Gmel. Syst. Nat., 

 1468 (1791). Cribraria cernua Pers. Obs. Myc, i. 91 (1796). 



C. exilis Macbr. in Bull. Nat. Hist. Iowa, ii. 378 (1893). Dicty- 

 dium umbilicatum Schrad. Nov. Gen. PI., 11 (1797) ; Lister 

 Mycetozoa, 148. D. ambiguum Schrad. I.e. ? D. cernuum 

 Nees Syst. Pilze, 120, fig. 117 (1816) : Rost. Mon., p. 229 ; 

 Mass. Mon., 67. D. trichiodes Chev. Fl. Paris, i. 327 (1826). 



D. longipes Morgan Myx. Miami Valley, 17 (1893). 



Var. 1. — fuscum Lister in Journ. Bot., xxxvi. 120 (1898) : 

 sporangia cernuous, smaller and browner than in the type, 

 with a well-defined cup from the margin of which the numerous 

 ribs arise. 



Var. 2. — alpinum Lister : sporangia usually erect, brown, 

 with or without an irregular cup ; ribs from twenty to thirty, 

 branching in the upper third of the sporangium to form an 

 irregular Cribr aria-like net ; stalk not narrowed at the apex, 

 often rugged. — Dictydium anomalum Meylan in Bull. Soc. 

 Vaud., xliv. 295. Heterodictyon mirabile Rost. Mon., p. 231 

 (1875). Cribraria mirabilis Mass. Mon., 60 (1892). 



PI. 147. — a. to d. sporangia of various forms after the dispersion of the spores ; 

 a. typical form ; b. var. fuscum ; c. form with irregular net found with sporangia of 

 usual type (England) ; d. erect sporangium (United States) ; e. spores, three of them 

 show plasmodic granules adhering ; /. g. sporangia of var. alpinum (type of Heterod- 

 ictyon mirabile Rost., from Freiburg) ; h. spores of same with plasmodic granules 

 adhering. 



The ribs of the sporangium-wall are usually inflexed at the summit in 

 maturity, and break the ball of enclosed spores by vertical pressure ; 

 they consist of two layers, the outer smooth and shining, the inner 

 studded'with purple plasmodic granules 1 \i diam. ; in the typical form 

 they are usually free at the base of the sporangium, but are sometimes 

 connected by a small basal disc. In large developments of this species 



