186 NEBRASKA STATE HORTICULTURAL SOCIETY. 



ordinary blight of twigs and leaves. In other cases it is due to 

 the presence of small worms (larvae) which eat the soft tissues 

 of the flower stalks and bases, killing the whole cluster much 

 as in the case of the blight. 



6. Fungi. Here we come to one of the most fruitful causes 

 of plant diseases. There are so many species of harmful fungi 

 that every kind of plant in which the fruit grower is interested 

 is infested by at least three or four, and some are attacked by 

 ten times as many. These affect trees in different ways but 

 for my present purpose I shall notice only the following modes : 

 («) Some grow over the surface of the leaves choking them so 

 that they can not jDerform their functions properly. A good 

 example of such a surface fungus is the Powdery Mildew, which 

 often attacks the leaves of nursery stock covering them with a 

 fine white powder. Every nurseryman knows that young trees 

 so affected can not make a good growth. The reason is that 

 the leaves can make the necessary food constituents, and as a 

 consequence the tree is partially starved. 



{h) Another type of fungus grows on the surface of fruits, 

 forming patches and blotches which are unsightly. The com- 

 mon 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 all kinds of plants grown by the 

 fruit grower. 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 I have seen leaves 

 in which one-tenth of their 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. It 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 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 



