196 



THE PLANT WORLD 



It is estimated that in the grain-raising states of the Middle West 

 668,338,000 bushels of grain have been destroyed by black stem 

 rust in the 13 years from 1915 to 1927 inclusive. This has meant a 

 yearly average loss of almost $55,000,000. The only way to prevent 

 this pest is to break the chain of the life cycle by destroying the 

 barberry bushes on which the spores grow in the spring of the year. 



recC spore 

 Hovm to 

 another stem 



Ted or 



summer- 

 rust on 

 M/heat stem 



barberry rust 



spore infecting* 



the cells ; of -wheat 



stem in 



Spring- 



through 

 ctSfaino; 



breo-t 

 pore. 



recTnrst , 



from stem fe steroJ 

 cCtrriMg" sum met* 



blorck or 

 -winter rust/ 

 lives on l 



straw through j 



infection fornix y@), S" ■■" v ?pL ^J~ If v-^-^ <-««-^ 

 ^^^^V -^Li O .lfir^in S | 0r<l 

 a cluster cup •V^** ' JJ^-v ^y V bocfxes , soorida 



^S&O a sporidium 

 W^T° infects the 

 jf cells of or 



barberry leaf. 



The life history of wheat rust. How would you go to work to exte 

 this pest ? Explain. 



te 



Blister rust. The pine tree blister rust is a recent importation 

 from Europe that threatens our white pine forests. This rust 

 passes one stage on the currant and gooseberry, so that the only way 

 to control it is to remove all currant and gooseberry bushes from 

 the neighborhood of such trees. 



Mildews. Another group of fungi that are of considerable 

 economic importance is made up of the sac fungi. Such fungi 

 are commonly called mildews. Some of the most easily obtained 



