DICTYDIUM 173 



sporangium," but here are forms in which the stem is ten times 

 the diameter of the sporangium, which yet possess in all other 

 particulars the characters of the short-stemmed forms. Euro- 

 pean forms also vary. Massee figures one type ; Lister, one or 

 two others ; Rostafmski's figure indicates a taller form ; Fries 

 says, "Stipes elongatus, peridio quinquies et ultra longior." It 

 seems reasonable to suppose that the variation in color is largely 

 due to atmospheric conditions at the time of fruiting. The 

 purple forms may be cases of arrested development, since the 

 plasmodium appears to be in all cases purple, or at least they 

 seem to represent those plasmodia which have failed of normal 

 maturation. Exposure to light has also much to do in deter- 

 mining final color. Forms developed in obscure places are less 

 differentiated in this respect. It would seem reasonable to seek 

 a ground of division in the structure of the net, the number of 

 the ribs, the coarseness or fineness of the meshes, but this ap- 

 pears to be entirely inconstant in specimens arising from the 

 same plasmodium. It may perhaps simplify matters to recog- 

 nize two general types, distinguished primarily by color : - 



a. D. cancellatum cancellatum. Sporangia clear brown or 

 with only a purplish tinge, the stipe tapering upward, and in 

 extreme cases perfectly white at the twisted apex. The stipe 

 in length ranges from three to ten times the diameter of the 

 sporangium. The reticulations of the net are generally small 

 and the ribs numerous. This is the most highly differentiated, 

 finished type of the species. 



b. D. cancellation purpurcum. Sporangia dark, the purple 

 tints predominating, the stipe tapering upward, more or less 

 twisted at the paler, sometimes almost colorless, apex. The 

 stipe ranges a little shorter than in the preceding variety, three 

 to seven times the sporangium. The reticulations of the net 

 are often coarse, the ribs being fewer ; the whole structure weak 

 and showing signs of imperfect development. 



Common everywhere. The fruit appears in June on decaying 

 logs and stumps of various species of deciduous trees, conifers, 

 etc. 



