FUNGI AND PLANT DISEASE 431 



trunk, causing a canker or swelling, and ultimately death. 

 Originally imported from Europe, this disease has attacked 

 successively three of the outstanding American timber trees; 

 the eastern white, western white, and California sugar pines. 

 Since the fungus must spend a part of its life history upon some 

 wild or cultivated currant or gooseberry, elimination of the alter- 

 nate host makes control of the disease possible. 



The CEDAR- APPLE RUST is a destructive organism on apple 

 trees in the east and midwest, causing early leaf fall, as well as 

 rusted, dead areas on the fruit. In addition to producing mal- 

 formed fruit, the tree is weakened and rendered more susceptible 

 to winter injury. The red cedar tree is alternate host to this 

 pathogen, and while ordinarily less severely damaged than 

 apples, the trees may become so heavily galled that their branches 

 are malformed or even killed. 



A third group of Basidiomycetes is known as the fleshy fungi. 

 This includes the gill fungi, of which our common edible field 

 mushroom is an example, and the pore fungi, to which belong 

 many of the bracket or shelf fungi so common on tree trunks. 

 Many of the organisms are saprophytic, living on dead wood and 

 fallen leaves, but many others are very destructive wood rots of 

 Uving forest trees. The saprophytic forms are important as 

 destroyers of such manufactured wood products as railroad ties, 

 posts, poles, mine timbers, and bridges. The preservative treat- 

 ment of woods to be used in these situations aids greatly in reduc- 

 ing the destructiveness of fungus activity. There remains, 

 however, the problem of reducing the losses due to wood rotting 

 fungi in forest trees, since this is an appreciable factor in 

 hastening depletion of American forest resources. Control 

 measures will probably be improved upon as forest products 

 become more valuable and as forestry practice increases in 

 intensity. 



A gill fungus known as mushroom root rot, which lives as a 

 saprophyte on logs, stumps, etc., may become parasitic, entering 

 forest and fruit trees through wounds in the roots, and penetrating 

 healthy underground tissues of potatoes and dahlias. Once inside 

 the host, this organism interferes with proper root functions and 

 ultimately results in its death. The parasite may be controlled by 



