INTRODUCTORY 5 



upon the ground, to flow in a hundred tiny streams over all the 

 region round about, to climb all stems, ascend all branches, 

 even leaves and flowers, to the height of many inches, all to 

 pass suddenly as if by magic charm into one widespread, dusty 

 field of flying spores. Or, to be more exact, whatever the 

 position ultimately assumed, the plasmodium soon becomes 

 quiescent, takes on definite and ultimate shape, which varies 

 greatly, almost for each species. Thus it may simply form 

 a flat, cake-like mass, (Bthaliiim, internally divided into an 

 indefinite number of ill-defined spore cases, sporangia ; or the 

 plasmodium may take the form of a simple net, plasmodiocarp, 

 whose cords stand out like swollen veins, whose meshes vary 

 both in form and size ; or more commonly the whole proto- 

 plasmic mass breaks up into little spheroidal heaps which may 

 be sessile directly on the substratum, or may be lifted on tiny 

 stems, stipitate, which may rest in turn upon a common 

 sheet-like film, or more or less continuous net, spreading 

 beneath them all, the JiypotJiallus. In any case, each differ- 

 entiated portion of the plasmodium, portion poorly or well 

 defined, elongate, net-like, spheroidal, elliptical, or of whatever 

 shape, becomes at length a sporangium, spore case, receptacle 

 for the development and temporary preservation of the spores. 1 

 The Slime-moulds were formerly classed with the gasteromy- 

 cetous fungi, puff-balls, and in description of their fruiting 

 phase the terms applicable to the description of a puff-ball 

 are still employed, although it will be understood that the 

 structures described are not in the two cases homologous ; 

 only analogous. The sporangium of the Slime-mould exhibits 

 usually a distinct peridium, or outer limiting wall, which is at 

 first continuous, enclosing the spores and their attendant 

 machinery, but at length ruptures, irregularly as a rule, and 

 so suffers its contents to escape. The peridium may be double, 

 varies in texture, color, persistence, and so forth, as will be 

 more fully set forth in the several specific descriptions. The 

 peridium blends with the hypothallus below when such struc- 



1 See, however, Ceratiomyxa, p. 17, following. 



