52 



Minnesota Plant Life. 



may find their way to the leaves of the barberry. When they fall 

 upon the epidermis of such leaves they develop infection tubes, 

 penetrate the skin and form a filamentous plant body \\ithin 

 the soft inner tissues. At their time of fruiting they form two 

 sorts of fruits, one upon the under side of the barberry leaves, 

 known as cluster cups, the other, peculiar bottle-shaped fruits, 

 upon the upper side. In the cup-shaped fruits large num1)ers 

 of spherical orange-colored spores are produced which if blown 

 away to a wheat field will infect the wheat. In the bottle- 

 shaped fruits smaller elongated spores are formed, but it is not 

 known how these germinate nor what becomes of them in the 

 natural order of events. Barberries are by 

 no means abundant in Minnesota, only a few 

 of them existing in hedge rows, and while it 

 iX ^' ' \ is by no means inconceivable or absurd, on 

 ■^ '-' account of the winds which blow over the 



wlieatfields of the Northwest, to suppose that 

 iKU-berrics in the east might infect the wheat 

 in jNIinnesota or the Dakotas, yet it is more 

 probable, I think, that the wheat-rust passes 



its cluster-cup stage 



on some common 

 Minnesota plant 

 which has not yet 

 been identified as 

 maintaining this 

 particular kind of 

 rust, or that it omits 

 altogether its cus- 

 tomary migrations 

 to other plants. 

 It is apparent that such a disease as the rust ofi'crs difiiculties 

 to the economic farmer desirous of protecting his crop, far in 

 excess of those presented Ijy the smut, for while smut spores 

 caught in the ends of the wheat kernels can he killed there by 

 hot water, no practicable method exists of policing the atmos- 

 phere and preventing rust spores from finding their way to the 

 young wheat. Therefore, the most feasible plan for combatting 

 wheat rust is i^y the (k'\ clopmcnt of so-called "rust proof" A'a- 



FlG. 13.— Wheat-r\ist in its barberrj-lt-af stage; to the left a 

 barberrj' leaf with diseased spots; in the middle, a sin- 

 gle spot with cups; to the right, two of the cups, in top 

 view slightly magnified. After Atkinson. 



