a teacher's knowledge of plant pathology. 
195 
The reason is that the leaves cannot make the necessary food 
constituents, and as a consequence the plant is partially starved. 
(&) Another type of fungus grows on the surface of fruits, 
forming patches and blotches which are unsightly. The common 
Apple Scab is a familiar example of a fungus of this kind. It 
is a surface fungus, never penetrating deeply into the tissues of 
the apple, but producing such disfigurement as to seriously injure 
its market value, (c) Still another type of fungus is that which 
lives inside of the leaf tissues, killing small patches. Such are 
the many Leaf-Spot fungi, of which many species are known 
to be parasitic upon many kinds of trees. Now the damage 
done by fungi of this kind is directly proportional to the amount 
of tissue killed in each leaf. In case of the shot-hole fungus 
(which kills little round patches on the cherry and plum leaves— 
the dead patches soon falling out and leaving holes) I have seen 
leaves in which one-tenth of the tissue was killed, which implies 
that the leaves had only nine-tenths of their full power to make 
food for the use of the tree. This is equivalent to reducing the 
food of the tree by just that amount, (d) There is still another 
type of fungus which lives inside of some part of the tree and 
decays it. Such fungi are among the most destructive with 
which we have to deal, and unfortunately they are very abundant. 
Some of them enter the root where it is wounded, and penetrate 
and rot the wood, turning it into a soft, dry, rotten mass. Here 
is where the evil effects of mutilation of the roots are manifest. 
Where a tree has rotten roots it cannot secure a sufficient supply 
of water and food matters from the soil, so that it suffers from 
thirst and starvation, while at the same time it is liable to still 
greater injury by being blown over by severe winds. Allied to 
the fungi which produce root-rot, and possibly identical with 
them, are those producing stem-rot. They gain access through 
wounds, and penetrate the stem tissues, turning them into a mass 
of decay. Aside from weakening the stem, which makes them 
especially liable to injury in high winds, the trees so attacked 
show evidence of general thirst and starvation. 
Many fruits are attacked by rot-producing fungi, as in the 
common apple rot, where a fungus gains entrance through some 
