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BOTANY 



(Fig. 52, T) and coalesce, forming small plasmodia (Fig. 52, m), which in turn fuse 

 with others into larger plasmodia (Fig. 52, n). Both the amcebse and plasmodia 

 are nourished by the small food particles taken up by the protoplasm, which also 

 exhibits active, internal, streaming movements. After an interval of a few days 

 the Plasmodium creeps to the surface of the substratum to the air and light, and 

 passing into a resting stage becomes at length converted into a white sporangium 

 with a double wall, consisting of an outer, calcareous, brittle peridium and an 

 inner and thinner enveloping pellicle which, in addition to the numerous spores, 

 encloses also a poorly developed capillitium. 



The development of the other Myxomycetes is accomplished in a similar 

 manner. Very large plasmodia, often over a foot in breadth, of a bright yellow 

 colour and creamy consistency, are formed by the tan-pit Fungus Fuligo varians 

 (Acthalium septicum), and as the "flowers of tan" are often found in summer on 

 moist tan bark. If exposed to desiccation, the plasmodia of this Myxomycete pass 

 into a resting state, and become converted into spherical or strand-like solekotiaJ 

 from which a plasmodium is again produced on a further supply of water. 

 Finally, the whole plasmodium becomes transformed into a dry cushion or cake- 

 shaped fructification of a white, yellowish, or brown colour. The fructification, in 

 this instance, is enveloped by an outer calcareous crust or rind, and is subdivided 

 by numerous internal septa. It encloses numerous dark violet-coloured spores, 

 and is traversed by a filamentous capillitium, in which are dispersed irregularly- 

 shaped vesicles containing granules of calcium carbonate. A fructification of 

 this nature, or so-called sethalium, consists, therefore, of a number of sporangia 

 combined together, while in most of the Myxomycetes the sporangia are simple 

 and formed singly. 



The structure and nature of the sporangia afford the most convenient means of 

 distinguishing the different genera. The following species may be mentioned as 

 exhibiting characteristic differences in the form of their sporangia. 



Stemonitisfusm forms simple, stalked, cylindrical sporangia (Fig. 222, A), which 

 are often found standing in clusters on dead leaves, bark, etc. The stalk is pro- 

 longed as a columella through the 

 sporangium, and gives rise to a deli- 

 cate, reticulate capillitium, within 

 the meshes of which lie the dark- 

 violet spores. The p er idium is thin 

 and non-persistent. Arcyriapunicea 

 produces its spherical sporangia on 

 rotten wood. They are simple, 

 stalked, of a reddish-brown colour, 

 and without a columella. At ma- 

 turity the peridium ruptures circu- 

 larly and the upper part falls off, 

 whereupon the capillitium attached 

 to the basal walls of the sporangiun 

 springs out suddenly, and sets free 

 the spores (Fig. 222, B). Cribraria 

 rufa also develops its reddish- 

 brown sporangia on rotten stumps of 

 trees. They are simple and stalked, without either columella or capillitium. The 

 sporangia open at the top, but the thickened portions of the fragile peridium 

 persist after its rupture in the form of a net-work (Fig. 222, G). Leocarpus fragilis, 



Fig. 222. — Ripe fructifications, after discharge of the 

 spores. A, Stemonitis fusca ( x 10) ; B, Arcyria 

 punicca (x 12) ; C, Cribraria rufa(x 32). 



