RHAMXUS IX THE DISSEMINATION OF CROWN RUST. 3 



As there is considerable difference between the various species of 

 buckthorn in regard to their behavior toward crown rust, each species 

 will be discussed separately. 



RHAMNUS CATHARTICA. 



Rhamnus cathartica L. is indigenous to northern Asia and therefore 

 is adapted to a cool climate. It is grown commonly throughout the 

 North Central States as an ornamental shrub or hedge plant, under 

 such popular names as buckthorn, hartshorn, rheinberry, and way- 

 thorn. Prior to the manufacture of barbed wire it was extensively 

 planted in hedges as a substitute for fences. It was not a success as 

 a fence, but, nevertheless, has found extensive use as an ornamental 

 shrub. 



The following places are the locations of some of the larger plant- 

 ings of R. cathartica in Iowa (fig. 1) : Boone, Clarion, Clinton, Council 

 Bluffs, Des Moines, Dubuque, Forest City, Harlan, Hinton, Iowa City, 

 Marshalltown, Monticello, Muscatine, Onawa, Whiting; and in Alla- 

 makee, Kossuth, and Pottawattamie Counties. 



The general use of R. cathartica through, a long period of time has 

 ; afforded ample opportunity for it to escape into wood lots and waste 

 lands. As this species bears abundant fruit each year it is probable 

 that the birds and winds have been active agents in its distribution. 

 Noteworthy occurrences of escaped shrubs have been found in Wis- 

 consin, Minnesota, South Dakota, Illinois, and Iowa, often in close 

 proximity to oat fields. 



OCCURRENCE AT HINTON, IOWA. 



In July, 1920, the attention of the writer was called by Dr. I. E. 

 Melhus to a severe epidemic of crown rust at Hinton, Plymouth 

 County, Iowa. This case was conspicuous because of the extent of 

 the Rhamnus plantings and the numerous adjacent fields of oats. 

 Northwest Iowa is fast becoming a chief oat-growing section of the 

 upper Mississippi Valley. Out of 2,980 acres which were surveyed in 

 detail in this locality, 1,020 acres were sown to oats. Many varieties 



\ . $rere grown, the most common of which were Albion (Iowa 103), 

 Richland (Iowa 105), Green Russian, and Silvermine. All of these 

 varieties show some degree of susceptibility to crown rust. 



An investigation of the cause of this epidemic was made, and a 

 buckthorn hedge 520 rods long was found. An 80-acre farm in sec- 

 tion 18 of Lincoln Township was completely surrounded by a hedge 

 from 10 to 20 feet high, while the adjacent section 7 in the same 

 township had about 80 rods of hedge. By questioning neighboring 

 farmers it was learned that this hedge was planted about 50 years ago 

 and that the oats grown near it had been severely rusted in many 

 seasons. No definite data were obtainable for previous years, but in 



J §1920, owing to an early epidemic of crown rust, the oat crop near the 

 nedge was worthless. Indeed, much of the crop was not harvested 

 because many of the plants did not head. 



In 1921 a detailed study was made on the rate and distance o( 

 spread of crown rust from the infected Rhamnus shrubs in this hedge. 

 The first pyenidia appeared on the leaves on May 13. The first 

 secidiospores were mature on May 16, and they were present in great 

 abundance by May 17. From one to five secidial cluster cups were 



