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 hyphac, 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 chicfly on certain nuclear phenomena. which 
