AECIAL STAGE OF PUCCINIA OXALIDIS 
W. H. Lone anv R. M. Harscu 
In July 1915 the junior writer collected an undescribed Aecidium 
on the leaves of Berberis repens in Bear Canyon, located in the 
Sandia Mountains about 15 miles east of Albuquerque, New Mexico. 
At the time the Aecidium was discovered no clue was found as to 
what hosts might harbor the alternate stages of this rust. The 
marked differences in the microscopic characters of the new 
Aecidium easily separated it from the aecial stage of both Puccinia 
graminis and P. koeleriae, the only two other rusts known to occur 
on species of Berberis. The first assumption was that this new - 
rust might have its alternate stage on some graminaceous host, but 
careful field work in the spring of 1916 by the senior author soon 
dispelled this theory, since this Aecidium was often found abun- 
dantly in localities where there were no possible grass hosts. Field 
observations showed that this rust always occurred in localities: 
where plants of Oxalis violacea and Berberis repens were closely 
associated, and when they were not associated no rust was found on 
the Berberis. Later in the spring of 1916 the senior writer found 
young leaves of Oxalis violacea bearing the primary urediniospores 
of Puccinia oxalidis in direct contact with the old aecia which had 
sporulated. This association of the two rusts was constant 
throughout the canyons in the Sandia Mountains, where the two 
hosts occurred in proximity to each other, while neither rust was 
found on either host when the hosts were widely separated. 
With this positive field clue as a guide, inoculations were made 
at Tejano Experiment Station, in the Sandia Mountains, about 
30 miles from Albuquerque, on 10 wild plants of Berberis repens 
growing in the open. After thoroughly wetting the plants, living 
old leaves of Oxalis bearing germinating teliospores of Puccinia 
oxalidis were placed above young leaves of Berberis. Both inocu- 
lated and check plants were protected by placing tin cans over them. 
These inoculations were made September 20, 1916. The tin cans 
were removed September 23. On October 20 the 10 inoculated 
475] [Botanical Gazette, vol. 65 
