INTRODUCTION 5 



stump. The mycelium may itself become reproductive in 

 various ways, but, in principle, it is the vegetative part of 

 the fungus. The true reproductive part is generally very 

 specialized, and in nearly all the fungi considered in this 

 book it has a marked form peculiar to each species of fungus, 

 and is (somewhat loosely) called the fructification. This 

 fructification bears a large number of spores or single, 

 generally very small, cells which are distributed by wind 

 or other agencies ; and each spore, if it falls on a suitable 

 feeding ground, is capable of producing a new mycelium, 

 which in its turn produces a fresh fructification. A familiar 

 fructification is a mushroom or any toadstool, which is 

 solely a reproducing organ, and is nourished entirely by 

 the mycelium, which is out of sight and buried in the soil. 

 The large bracket fungi found on trees are also fructifica- 

 tions, only these fungi differ from a mushroom in the fact 

 that their mycelium lives and grows in the trees instead of 

 in the ground. 



The fructifications of the fungi which grow on trees are 

 often very large, and when it is remembered that all the 

 food necessary to produce them is derived from the tree, it 

 will be clear that the tree must suffer accordingly. Frequently 

 the tree is killed, but if the fungus is a facultative and not 

 an obligate parasite, its growth will not immediately be 

 checked by the death of the tree, and not uncommonly 

 dead trees are a dangerous source of infection to living 

 ones. The tree or other plant on which a parasite grows 

 is somewhat unkindly called its host. 



When investigating the life -history of a fungus it is often 

 found that there is another form of reproduction besides 

 the fructification. In some species almost any part of the 

 mycelium may give rise to specialized hyphae, which bear 

 cells which are not unlike spores and have the same faculty 

 of reproducing the plant. These cells are given the dis- 

 tinguishing name of conidia, and the hypha that bears 

 them is called a conidiophore. The distinction between 

 spores and conidia has given rise to much controversy, and 

 is now based chiefly on certain nuclear phenomena which 



