BLACK STEM GRAIN RUST 



195 



Brownell 



Shelf fungi (Fomes applanatus as often seen growing on the 

 trunks of trees. They cause enormous losses by causing the 

 timber to decay. 



kill the tree and burn it, so as to destroy the spores. Each year 

 many fine trees, sound except for a slight bruise or other injury, 

 are infected and 

 eventually killed 

 by this fungus. 



Field Exercise. 



On a field trip we 

 may see a number of 

 trees which are in- 

 fected with fungi. 

 Count the number 

 of perfect trees in a 

 given area. Com- 

 pare it with the 

 number of trees at- 

 tacked by fungus. 

 Does the fungus ap- 

 pear to be trans- 

 mitted from one tree 

 to another near 

 at hand? In how 

 many instances can you discover the point where the fungus first at- 

 tacked the tree? How do the spores leave the spore case? How do 

 they germinate on the tree which they attacked? 



Black stem grain rust. Wheat rust is probably the most destruc- 

 tive parasitic fungus. For hundreds of years this rust has been 

 the most dreaded of plant diseases, because it destroys the one 

 harvest upon which the civilized world is most dependent. For 

 a long time past the appearance of rust has been associated with 

 the presence of barberry bushes in the neighborhood of the wheat 

 fields. Although laws were enacted in 1760 in New England to 

 provide for the destruction of barberry bushes near infected wheat 

 fields, nothing was" actually known of the relation existing be- 

 tween the rust and the barberry until comparatively recent years. 

 It has now been proved beyond doubt that the wheat rust 

 passes' part of its life as a parasite on the common barberry and 

 from there gets to the wheat plant, where it undergoes a compli- 

 cated fife history. The wheat leaf, its nourishment and living 

 matter used as food by the parasite, soon dies, and no grain is 

 produced, 



