148 BNDOSPORE^. [dICTTDIUJ 



SPECIES EXCLUDED FROM THE GENUS. 



G. nvirahiUs Mass. = Bictydium umhilicatvm Schrad. 

 C. exiUs Macbride = Dictydium umhilicatum Schrad. 



Genus 24.— DICTYDIUM Schrader, Nov. Gen. PL, p. 11 (1797 

 Sporangia globose, stipitate ; sporangium- wall formed of parall 

 ribs extending from the base to the apex, connected by slend( 

 transverse threads, the intervening wall evanescent. 



1. D. umbilicatum Schrad., I.e., p. 11 (1797). Plasmodiui 

 purple. Total height 1 to 2 mm. Sporangia globose, cernuou 

 0'5 to 0'7 mm. diam., dark red-brown ; sporangium-wall formir 

 a net with nearly square meshes, composed of numerous rigi 

 longitudinal ribs 5 /a thick, connected by delicate transvers 

 threads ; basal cup scarcely developed. Stalk subulate, bent < 

 twisted at the slender apex, rich purple-brown, one to thr( 

 times the length of the sporangium. Spores pale red, minute] 

 warted, 4 to 7 yu. diam., usually with two to four purple plasmod 

 granules on the spore wall. — Pr., Syst. Myc, iii., p. 165. Muct 

 cancellatus Batsch, El. Fung., ii., 137 (1786). Stemonitis cw. 

 cellata Gmel., Syst. Nat., p. 1468. Cribraria cernua Pers., Ob 

 " Myc, i., p. 91 (1796). Dictydium cernuum Nees, Syst. Pilz< 

 p. 120 (1816) ; Host., Mon., p. 229 ; Cooke, Myx. Brit., p. 5'i 

 Blytt, Bidr. K. Norg., Sop. iii., p. 9 ; Macbride, in Bull. Nat. His 

 Iowa, ii., p. 118. Hetertdictyon mirahile Eost., Mon., p. 23 

 Grihra/ria mirabilis Mass., Mon., p. 60. G. exilis Macbride; : 

 Bull. Nat. Hist. Iowa, ii., p. 378. 



Plate LVI., B. — a. to d. sporangia of various forms after the dispersion 

 the spores, x 36 ; a. typical form ; i. form with cup ; c. form with irregul 

 net, found with sporangia of usual type (England) ; d. erect sporangin 

 (United States) ; e. spore, x 600 ; /., g. type of lieterodictyon mwah 

 Eost., X 70 (Freiburg, Germany) ; h. spores of same, x 600. 



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

 maturity, and break the ball of enclosed spores by vertical pressuri 

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

 beset with purple plasmodic granules 1 ^ diam. ; they are usually fr 

 at the base of the sporangium, but are sometimes connected 1 

 an irregular basal disc. A form is occasionally found with a we 

 developed cup having an evenly toothed margin from which the ri 

 take rise ; associated with this character the stalk is more erect, a] 

 of a browner colour than in the usual type ; the variety, howev( 

 appears to be too inconstant to be marked as distinct. A carei 

 examination of the type specimen of Eeterodictyon mirabile Ros 

 in the Strassb. Herb., leads to the conclusion that it is a form 

 Dictydium umhilicatum. It is no doubt a remarkable developmen 

 the basal cup is large and irregular, and the ribs in many parts a 

 expanded and form a loose, imperfect net with broad and angul 

 nodes; in other parts the ribs are connected by the usual delicE 

 transverse threads, and though fewer in number and coarser than 

 the type, are essentially of the same character ; they are thickly bes 

 on the inner side with purple plasmodic granules, the cup is al 

 studded with the same ; the spores are precisely similar to those 



