Minnesota Plant Diseases. 41 



heart-wood through a wound in the bark but never attack the 

 sap wood. Some half-saprophytes are capable of attacking the 

 sapwood after an established saprophytic life thus becoming 

 parasitic in habit. Such fungi are known as wound parasites. 

 They live most of their lives as saprophytes and are capable of 

 living for an indefinite time as such. The wound parasites are 

 dangerous enemies to forest and shade trees. The injuries and 

 wounds through which fungi gain entrance to a living tree may 

 be caused in numerous ways which will be more fully discussed 

 later. Storms, hail, insects and rodents are among the more 

 common agencies. 



Leaf-dwelling habit. There is a great host of very minute 

 fungi found on dead leaves, while the latter are still on the tree 

 or after they have fallen. For the most part they are "burnt 

 wood" fungi but one often finds among them small fungi of 

 the mushroom group. In fact, most of those fungi found on 

 the leaf mold of our forest floor are in reality leaf saprophytes. 

 The number of such plants is very large and includes fungi of 

 very different kinds. Most conspicuous, perhaps, are the fleshy 

 fungi of the mushroom group which, on the undisturbed floor 

 of the hard-wood forests in the northern part of the state, often 

 occur in astonishing abundance. The burnt wood fungi are 

 also very abundant. 



The leaf saprophytes, as well as the wood saprophytes, are 

 of great importance in nature's economy, for they are the 

 agents through which the dead plant structures are gradually 

 disintegrated or broken down until finally the constituents are 

 again mingled with those of the soil and air. The substances 

 are actually burned by this process until they arc reduced t 

 soil and air constituents. If this fungus and bacterial disinte- 

 gration of wood and leaves were suddenly to cease all over the 

 world the earth's surface would quickly be cove-red with the 

 debris of leaf-green plants and its physiognomy would be vastly 

 changed. Many of the plants of this day would require impor- 

 tant alterations in their habits and form to survive such a 

 change, as they would at present be unable to exist among the 

 fast accumulating debris. Plants of low stature on the fores! 

 floor would probably succumb first and if one imagines the 

 process to continue indefinitely only the taller plants would 



