14 BULLETIN 1162, U. S. DEPARTMENT OF AGRICULTURE. 



to develop in the area nearest the buckthorns. Numerous grasses 

 bordered this area, though Phleum pratense L. and Calamagrostis 

 canadensis (Michx.) Beauv. were the only two grasses which were 

 infected with crown rust. The flora directly beneath the Rhamnus 

 shrubs consisted largely of sedges. 



At still another location, about 7 miles removed from this field 

 Phleum pratense, Calamagrostis canadensis, Sphenopolis (Eatonia) 

 obtusata (Michx.) Scribn., Agrostis hy emails (Walt.) B. S. P., and 

 Avena sativa L. were infected with crown rust when growing near 

 Rhamnus lanceolata. In addition, Festuca, elatior L. was found 

 infected with crown rust in 1921. Although many cases have been 

 inspected during the past five years, that at Indianola in 1919 is the 

 only one which gave positive evidence that R. lanceolata is instru- 

 mental in spreading the crown rust to oats under field conditions. 



Although aecidial infection occurs on this species at Osceola and at 

 Bloomfield, Iowa, each year, the situation at the latter place is dif- 

 ferent from those previously discussed. At Bloomfield, which is 

 in the extreme southern portion of the State, H. H. Plagge found 

 uredospore infection on oats in 1919 previous to the appearance 

 of secidial infection on R. lanceolata. It is probable that crown rust 

 here had hibernated as mycelium or in the uredospore stage, a rare 

 occurrence in Iowa. 



R. lanceolata is not used as a hedge or ornamental shrub and there- 

 fore is seldom found growing in the immediate vicinity of oat fields. 

 It should be noted also that the area comprising the habitat of this 

 shrub lies principally outside the main oat-growing section of the 

 Middle West. 



STUDIES IN ARKANSAS AND MISSOURI. 



From April 2 to 10, 1919, an extensive field study was made in the 

 vicinities of Fort Smith, Prescott, and Little Rock, Ark., to deter- 

 mine whether this shrub was instrumental in starting the annual 

 infection of crown rust in that section. At this time R. lanceolata 

 was just coming into leaf and no infection was evident, although 

 uredosori were common on winter oats. As crown rust often lives 

 over winter in Arkansas, this shrub seems to play only a minor role 

 in the initial appearance and subsequent dissemination of crown rust 

 there. 



iEcidial infection occurs on R. lanceolata in Missouri annually, as 

 shown by studies at Arlington. It was not found infected at Moun- 

 tain Grove, in the southern part of the State, during the springs of 

 1919 and 1920. Here, as in Iowa, the shrub seldom grows near oat 

 fields, and hence its opportunity for aiding the spread of crown rust 

 is not extensive. 



RHAMNJS CAROLINIAN A. 



Rhamnus caroliniana Walter is a native species extending eastward 

 from Texas, Kansas, and Missouri, the latter State being the northern 

 limit of its range. It is abundant on shaded hillsides and stony 

 ridges of eastern Kentucky and Tennessee. It most closely resembles 

 R. lanceolata, which it largely supplants in the southeastern section 

 of the United States. 



The hills surrounding Knoxville, Tenn., bear an abundant growth 

 of this shrub, varying in height from 6 inches to 30 feet or more. 



