162 



THE BOOK OF WHEAT 



to grow smutted wheat because it has always done so, and be- 

 cause the extent of the loss and the ease of its prevention are 

 so little realized. Formerly at least one-fifth of the cereal 

 crops was annually destroyed by smut. Smutty wheat intro- 

 duces a large element of speculation into the business of ele- 

 vator men, for it produces a very low grade of flour. Such wheat 

 must be washed, an expensive process which also endangers the 

 quality of the flour. From smutted flour the baker gets a poor, 

 darkened product that finds little market. As a result smutted 

 wheat is justly thrown into a very low, or "rejected" grade. 



Rust. What is popularly termed 

 wheat rust may be the result of 

 one or more of a number of rust 

 fungi, parasitic plants. This dis- 

 ease was mentioned by Virgil. It 

 was known in Britain before 1592. 

 Fontana (1767) is generally ac- 

 credited with connecting rust of 

 cereals with a specific fungus, 

 which Persoon (1797) investigated 

 more fully, and named. Three kinds 

 of rusts are known to attack wheat. 

 Puccinia coronata, the crown rust, 

 is comparatively unimportant. The 

 two distinctive rusts are Puccinia 

 orange leaf-rust, and P. gram- 

 inis, the late, stem-rust. The former is popularly called "red" 

 and the latter "black" rust. Both species, however, produce 

 first reddish and then black spores, but in the orange leaf-rust 

 the red spores are far more abundant than the black ones, while 

 in the stem-rust the black spores are the more abundant. 



LIFE HISTORY. The wheat rusts belong to that type of 

 fungi which have several stages of development represented by 

 different types of spore formation and separated by two or 

 more rest periods. The life history is the development of the 

 fungus through all its stages, and it is said to be "known" 

 when the experimenter can take one type of spore formation 

 and from this produce artificially all of the other types in 

 turn through the life cycle until a return is made to the type 

 of spore formation with which he began. Usually the types 



AECIDIA ON BARBERRY 



rubigo-vera, the early, 



