RHAMNUS IN THE DISSEMINATION OF CROWN RUST. 1 5 



Observations made in April, 1919, just as these shrubs wer£ coming 

 into leaf, showed no evidence of infection. Oats growing in an 

 adjoining field showed no uredospore infection. In July, however, 

 this field was heavily infected with crown rust, although there still 

 was no trace of secidial infection on the Rhamnus. Carl Kurtzweil 

 reported gecidial infection on Rhamnus at this location in 1920. 



Observations were made at Lexington, Ky., and in the Missouri 

 Botanical Garden at St. Louis in 1919, but no secidial infection was 

 present. Dr. Harrison Garman, in a personal conversation, said that 

 R. caroliniana was heavily infected at Lexington, Ky., and- Arthur 

 reported finding secidia on R. caroliniana in a garden at La Fayette, 

 Ind., in 1905. Although repeated search has been made, the w i 

 has never found aecidia on this shrub in the field. Plantings on the 

 campus at Ames, Iowa, have never developed Becidiospores, though 

 oats heavily infected with crown rust grew near the Rhamnus. 



Greenhouse experiments in which teleutospores from Avena saliva 

 were used as inoculum gave only pyenidia (8). However, in the 

 spring of 1922 a few cluster cups were formed on R. caroliniana in 

 the greenhouse trials with the teleutospores from Avena sativa. 



Because of the limited investigations made, the role of R. carolin- 

 iana in spreading crown rust of oats is thus far not well understood. 

 The data available suggest that it is not an important alternate host 

 for the specialized form of crown rust occurring on the cultivated oat. 



RHAMNUS ALNIFOLIA. 



Rhamnus alnifolia L'Her., or dwarf alder, which is largely confined 

 to swamps and shaded banks of streams, is primarily a northern 

 species, reaching the southern limits of its distribution in the 

 northern portions of Iowa, Nebraska, and Illinois. In Iowa it has 

 been collected at Decorah and along the Yellow River in the north- 

 eastern part of the State. It grows abundantly also in Door county. 

 in northeastern Wisconsin. About 25 oat fields were inspected in 

 that county, but crown-rust infection was almost entirely absent. A 

 maximum infection of 10 per cent was found, but this was confined 

 to a few small local patches. 



In the lowlands surrounding Sturgeon Bay, Wis.', R. alnifolia grows 

 in great profusion. The grass flora of this locality consists mostly 

 of Calamagrostis canadensis, which occurs beneath these shrubs and 

 often extends to the edge of the lowlands where oats are grown. This 

 locality has been under observation for the past four years to deter- 

 mine the possible relationship between the secidial infection on this 

 buckthorn and the uredospore infection on oats. Abundant teleuto- 

 spore and uredospore material on Calamagrostis has been collected 

 there in every year except 1920, when the infection was light. 



On May 24, 1919, Calamagrostis canadensis infected with uredo- 

 spores of crown rust was growing in the vicinity of R. alnifolia at 

 Sturgeon Bay, Wis. The Rhamnus at this time was just coming 

 into leaf and showed no traces of infection. Greenhouse tests 

 have shown that crown rust on C. canadensis is only occasionally 

 able to infect oats. Although it was evident that secidia on R. alni- 

 folia were directly responsible for infection on Calamagrostis, this 

 buckthorn probably does not act as a direct agent in the distribution 

 of crown rust to oats. 



