1] Introduction to Fungi 15 
The various fungi behave very differently on 
different plants and also in their manner of attack. 
The mycelium of the potato disease fungus kills the 
cells with which it comes in contact and then dies; 
the living mycelium occurs only in and near the region 
of living cells. 
In rusts the mycelium lives together with the 
protoplasm of the cells and both take their food from 
the same source. 
The mycelium of the smut fungi lives with the 
young cells at the tips of the shoots without killing 
them. When however it enters the grain all the cells 
of the grain are used up and the mycelium produces 
spores. 
In the case of “finger and toe” in turnips, the 
cells containing the fungus not only do not die but are 
stimulated to increased growth with the result that 
they are much larger than the surrounding cells which 
contain no fungus. 
Some fungi live on one kind of plant only and 
are apparently incapable of living on others. Other 
fungi live only on plants belonging to a certain natural 
order. Others again live on a very large number of 
plants belonging to different orders. Rotation of crops 
is often very effective in keeping diseases in check, 
since a fungus disease of one crop is often incapable of 
attacking the following crop and may die out before a 
suitable host crop is grown. But if suitable weed 
hosts are present the disease may be carried on for an 
indefinite period. In some cases the fungus may have 
to travel a considerable distance before reaching a 
suitable host. 
Our present system of marketing in which empties 
