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



Rhamnus lanceolata Pursh is perhaps the most widely distributed 

 native species. It occurs commonly from eastern Nebraska across 

 south-central Iowa to Pennsylvania and southward to Florida. It 

 is not used as an ornamental shrub and seldom grows near cultivated 

 fields. Though it bears aecidia every year, the case at Indianola, 

 Iowa, is the only one known to the writer where this species was 

 responsible for the initial infection of crown rust of oats. 



^Ecidiospores collected on R. lanceolata were capable of infecting 

 PMeum pratense, Calamagrostis canadensis, AgrostU hyemalis, and 

 Festuca elatior under field conditions. As uredospores overwinter in 

 the South, it is probable that this species plays little part in the 

 initial infection by crown rust there. 



Rhamnus caroliniana is another native species, extending eastward 

 from Texas, Kansas, and Missouri to the Atlantic coast. Apparently 

 it does not bear secidiospores every year, but in recent greenhouse 

 experiments cluster cups were produced when it was exposed to 

 infection by teleutospores from oats. R. alnifolia is a native northern 

 species bearing heavy secidiospore infection of crown rust where 

 Calamagrostis canadensis grows near it. Although it has been found 

 to aid the spread of crown rust to this grass, no case is known where 

 it was a factor in spreading the specialized form of crown rust which 

 occurs on oats. 



Five other species of buckthorn, one introduced and four native, 

 namely, R. frangula, R. smithii, R. purshiana, R. calif ornica, and 

 R. crocea, are relatively unimportant in the dissemination of crown 

 rust to oats. R. frangula has escaped from cultivation in the north- 

 eastern United States. 



The others are species of very limited distribution in the far West 

 and usually distant from fields of oats. R. smithii and R. purshiana 

 bear secidia under field conditions, and grasses near the former species 

 become infected. 



LITERATURE CITED. 



(1) Bary, A. de. 



1866. Neue Untersuchtingen liber die Uredineen . . . In Monatsber. 

 K. Preuss. Akad. Wiss. Berlin, 1865, p. 15-49, 1 pi. Biblio- 

 graphical footnotes. 



(2) Britton, Nathaniel Lord. 



1907. Manual of the flora of the Northern States and Canada. Ed. 3. xxiv, 

 1122 p. New York. 



(3) Eriksson, Jakob. 



1894. Ueber die Specialisirung des Parasitismus bei den Getreiderostpil- 

 zen. In Ber. Deut. Bot. Gesell.. Bd. 12, p. 292-331. Litteratur- 

 verzeichniss, p. 330-331. 



(4) 1904. Ueber das Vegetative Leben der Getreiderostpilze. I. K. Svenska 



Vet. -Akad. Ilandl., Bd. 37, no. 6, 19 p., 3 pi. 



(5) Henning, Ernst. 



1894. Nasjra ord om olika predisposition for rost a, sad. In K. Landtbr. 

 Akad. Handl. och Tidskr., Arg. 33, p. 205-217. 



(6) 1921. Rhamnus cathartica bor icke odlas. (Rhamnus cathartica ought not 



to be cultivated). In Svensk. Land. No. 5. 



(7) Klebahn, H. 



1892. Kulturversuche mit heterocischen Uredineen. In Ztschr. Pflanzen- 

 krank., Bd. 2, p. 332-343. Bibliographical footnotes. 



(8) Melhus, I. E., Dietz, S. M., and Willey, Florence. 



1922. The alternate hosts and biologic specialization of crown-rust in Amer- 

 ica. Iowa Agr. Exp. Sta. Research Bui. 72, p. 211-236, 2 fig. 

 Bibliography, p. 235-236. 



