16 BULLETIN 1162, U. S. DEPARTMENT OF AGRICULTUKE. 



FIVE LESS IMPORTANT SPECIES. 



Various factors and combinations of factors cause Rhamnus frangula, 

 R. smithii, R. purshiana, R. californica, and R. crocea to be less 

 important in the dissemination 01 crown rust to oats than are the 

 species previously mentioned. These species of Rhamnus have a 

 limited distribution and their habitats lie principally outside of the 

 oat-producing sections. They frequently are found at high altitudes, 

 far removed from cultivated fields, which precludes the possibility of 

 their becoming infected under ordinary field conditions. 



RHAMNUS FRANGULA. 



Rhamnus frangula L., commonly known as black alder, berry alder, 

 and arrowwood, is a native of Europe. It often is used in the United 

 States as a hedge and ornamental plant and has escaped commonly 

 in bogs and wet places on Long Island, in northern New Jersey, and 

 in Ontario, Canada, according to Britton {2). It is not common in 

 the Middle West, but has been reported by J. B. Mayer as escaped 

 from cultivation at Hull, Iowa, which is the only place known to the 

 writer where R. frangula occurs as an escape in Iowa. 



According to greenhouse trials (8) R. frangula developed pycnidial 

 infection, but never secidial infection, when exposed to teleutospores 

 from species of A vena and Calamagrostis, two of the most widely 

 distributed crown-rust hosts in the oat-producing region. The escaped 

 plants near Hull in the northwestern part of the State and cultivated 

 plants at the Missouri Botanical Garden in St. Louis both have been 

 inspected, but there was no aecidial infection at either place. Although 

 but limited observations have been made, it seems probable that R. 

 frangula is of little importance in the dissemination of crown rust in 

 the Middle West. 



RHAMNUS SMITHII. 



Rhamnus smithii Greene, a thick-stemmed dwarf shrub bearing 

 lanceolate leaves, is confined to a few thousand acres near Pagosa 

 Springs in southwestern Colorado, where it grows very abundantly. 

 It is rarely found near cultivated fields. It is cultivated in Boulder, 

 Colo., where it thrives and often reaches a height of 12 feet. 



At Pagosa Springs, Colo., a relatively high percentage of secidial 

 infection was present in 1920 and 1921. 



Teleutospores of crown rust were collected at that place on Agro- 

 pyron smithii, Koeleria cristata, Bromus ciliatus, and Trisetum sp. by 

 Miss Florence Willey in July, 1921. Shrubs of R. smithii growing 

 near these grasses were heavily infected. Later in the season uredo- 

 spores were collected on Bromus sp. growing beneath heavily infected 

 bushes. Although the relationship of this alternate host to these 

 grass species must be verified by controlled greenhouse study, it is 

 probable that it is not of much importance in spreading crown rust 

 to oats, as little of this cereal is grown in the vicinity. Its response 

 to infection with teleutospores from oats under greenhouse conditions 

 (8) suggests its close relationship to R. lanceolata. It may be that 

 R. smithii is only a form of R. lanceolata which has become adapted 

 to the high altitudes of the Rocky Mountain region. 



