GRA.SSES OP IOWA. 273 



' 'In this region Onosomodlum carolinanum bears very profusely 

 an eecidium, which, because of its date of appearance, was 

 worthy of suspicion; but tests enough were made to remove 

 this notion. " P. rubigo-vera as well as the common grass rust, 

 is very destructive in England and Australia; according to 

 Wolf, not so common in Germany. A few years ago Professor 

 Arthur investigated the subject of wheat rust in Indiana and 

 found that this species was much more destructive to wheat in 

 that state than common grass rust. The same year, 1889, I 

 found that this rust was much more common on our wheat. 

 Carleton* says he is confident that the orange-leaf rust (P.rubigo- 

 vera) does very little if any damage to the grain in this country; 

 that in all cases of serious damage to the grain by rust the 

 black-stem rust (P. graminis) is the real cause. 



In 1891 and 1892 the rust under consideration was hardly as 

 destructive as common grass rust. In 1893 covered rust was 

 more abundant than common rust. Atkinson states that uredo 

 spores develop during any month of the year, during the win- 

 ter and spring attacking the grains, and during the summer and 

 autumn the grasses, so that we may probably have a perennial 

 infection from uredo spores, Bolley states that there are iso- 

 lated cases in which the mycelium of this species may live in 

 the tissues of the wheat during the winters. This, however, 

 can occur only during the mild winters. I have been unable to 

 verify this for the state of Iowa, and Bollej^ has, likewise, 

 failed in North Dakota. Hitchcock and Carleton find that in 

 the vicinity of Manhattan, Kan., the Puccinia rubigo-vera passes 

 the winters in the tissues of the wheat plant in the mycelial 

 condition. During the warm weather of spring a crop of spores 

 is produced which, under favorable conditions, may rapidly 

 spread the disease. The infection of the winter wheat in the 

 fall is materially aided by the volunteer wheat, which carries 

 the rust through the few months following harvest, and these 

 results have been reconfirmed by Carletonf in Kansas and 

 Maryland. According to Sorauerthe mycelium is perennialin 

 the parenchyma of the leaves of cereals. We are forced to the 

 conclusion that infection is general and that our wheat suffers 

 much from southern invasion of this parasite. No doubt the 

 perennial character of the mycelium in warm climates plays an 

 important part in spreading the disease. In northern states, 



♦Improvements in wheat culture. Year book U. S. Dept. of Agrl. 1896: 497. 

 tOereal rusts. 1. c. 21. 



17 



