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THE POPULAR SCIENCE MONTHLY, 



may bo simply wrinkled; sometimes it is warty or prickly, and in 

 Fig. 5 it is represented as covered with spines. Again, in some species 

 of fungi, tlie liymenium, instead of being situated externally, is in- 

 closed in a membrane which bursts when its spores are ripe, and 

 scatters them like a cloud of smoke to the winds. Of such is the 

 pufl-ball. Fig. 6, with which everybody is familiar. 



Fig. 5. Htdnxjm Eepandum. 



Fig. 6. Sclekoderjia Vulgaee. 



These fleshy forms, however, although very numerous, constitute 

 but a small part of this immense group. But most of the species in- 

 cluded in it are either quite invisible, or else the parts which charac- 

 terize them as fungi are so small as to be indistinguishable. The fea- 

 ture by wliich a fungus may always be known is the mycelium. Every 

 plant of which this structure forms a part, spreading its web through- 

 out the substance on, or in, which it grows, belongs among fungi. 

 They differ among themselves in such comparatively unimportant re- 

 spects as the mode of growth of the hymenium, or the degree of com- 

 plexity of tlie reproductive system, but mycclia and spore production 

 are their essential characters. In these diminutive organisms, the deli- 

 cate mycelium is so minute as to traverse living plants and the pores 

 of solid wood. The potato-rot is such a fungus a sort of mould the 

 mycelium of which grows rapidly, penetrating the leaves, stem, and 

 tubers, and causing quick decay. Dry-rot in timber is occasioned by 

 the penetrating mycelium of fungi. The yeast and vinegar plants are 

 submerged mycelia. The mildews, rusts, and smuts of grain those 

 scourges of the farmer are all fungi. Their minute mycelium pene- 

 trates and destroys the tissues of plants, and, bursting through the 

 cuticle, covers them with myriads of their orange, brown, and black 

 spore. All those black, pustular growths seen on dead wood, bark, 

 twigs, and leaves, and the whole tribe of moulds that cover every 

 substance exposed to dampness, are fungi. Not only do these fungi 

 ravage the living and the dead, but they fill the air with the cotmtless 

 myriads of their spores. These subtile particles, " invisible to the 

 naked eye, and light almost as vapor, are continually floating in the 

 air we breathe, or swimming in the water we drink, or lying amid the 

 imj^alpable dust and sand of the soil, waiting the presence of warmth 



