DRY-ROT IN TIMBER. 527 



amine the mold on which this singular plant is seen to grow, you will 

 find it penetrated with delicate, whitish, interlacing filaments which are 

 the vegetative system of the plant. This part of a mushroom is called 

 the mycelium, and from it arises the reproductive portion which grows 

 above ground. But the only part of this above-ground portion that is 

 essential, and that is found in all fungi whatever, is just that part 

 which escapes ordinary observation. Everybody has seen the umbrel- 

 la-like cap with the radiating vertical plates on its under surface. These 

 plates are covered by a membrane which has the same office as the 

 seed-vessel of the higher plants. It bears the minute reproductive 

 bodies of the fungi, analogous to common seeds, and called spores. 



The only parts of a mushroom which are common to all fungi are 

 the mycelium or thready, interlacing portion which grows underground, 

 and the minute, microscopic spores which are cellular in structure and 

 so small that thousands of them are required to form a body the size 

 of a pin's head. The fungi differ among themselves in many ways ; 

 but mycelia and spore production always occur in them, and are their 

 essential characters. Every plant of which this mycelium forms a 

 part, spreading its web throughout the substance on, or in, which it 

 grows, belongs among fungi. Most of the species are either quite in- 

 visible, or else their parts are so small as to be indistinguishable. But 

 some sort of reproductive organs exist, and spores are always produced. 

 The mycelium is often so minute as to traverse living plants and the 

 pores of solid wood. It grows rapidly and causes quick decay. Po- 

 tato-rot, the yeast- and vinegar-plants, mildews, rusts, and smuts of 

 grain, and molds of all kinds, are part of this immense group of 

 plants that lives upon decay and fills the air with its countless myriads 

 of spores. These subtile, germinal particles are lodged everywhere. 

 They are light as vapor and abound in air, in water, in dust, in sand, 

 ready, when warmth and moisture favor, to burst into life. As has 

 been said, the dry-rot fungi flourish upon the products of wet-rot. 

 Different stages of decay produce food of different qualities, adapted 

 to different species of fungi. One species takes up the process where 

 another leaves it, and carries it further and further forward. 



Dry-rot may begin its ravages in the interior of timber as easily as 

 upon the surface. As atmospheric dust is filled with the spores of 

 fungi, they may be conveyed by rain into the earth, absorbed by the 

 roots of vegetables, and diffused with the sap throughout the whole 

 plant. There are numerous species of dry-rot fungi adapted to differ- 

 ent conditions of life and presenting different aspects. Nor are they 

 restricted to timber. They may flourish in the earth, where they pre- 

 sent a perfectly white mycelium, branching and interlacing like roots ; 

 and when workmen are employed on grounds which are affected by the 

 dry-rot fungi their health is often disturbed. A few years since, while 

 a London builder was putting up some houses at Hampstead, his men 

 were never well. He afterward learned that the ground was affected 



