CHAPTER IV 
SAPROPHYTES AND PARASITES 
UNGI deriving their nutriment from dead organic 
X matter, such as dead leaves, wood, etc., are termed 
saprophytes; those which obtain their food from living plants 
and animals are known as parasites. Some species are able 
to accommodate themselves to either kind of diet. 
A spore from a parasitic fungus may germinate on what¬ 
ever it happens eventually to settle upon, but unless it does 
so on the host (or hosts) it particularly affects it will produce 
only a germ tube, and then die. There is something in the 
cells of its true host that it is specially fond of, something 
which attracts the germ tube and causes it to enter. Hence 
we understand why it is that a fungus producing myriads of 
spores is rare or uncommon. Perhaps only one spore in 
several millions germinates under favourable conditions and 
produces mycelium ; all the others, owing to unfavourable 
environment, die soon after germination. 
It has been demonstrated that a parasitic fungus can be 
induced to enter the leaves of a plant which is not its true 
host, and there produce its spores, by injecting the leaves 
with a substance much liked by the parasite. If the spores 
produced under these conditions are in turn sown upon 
other injected leaves, and the process continued for many 
generations, it will be found that the twenty-fifth generation 
(or thereabouts) is able to enter leaves that have not been 
injected with the attractive substance. The parasite has 
been gradually educated to feed upon and thrive on the 
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