rots] SHULL—XANTHIUM 483 
Xanthium population seems to be isolated according to species, 
there is always the possibility that the latest plants of one species 
may have the opportunity to cross with the earliest plants of a 
later blooming species. Such a cross between X. globosum and 
X. pennsylvanicum might possibly have given rise to X. canadense. 
At a later time, when the range of variability of X. globosum 
has been carefully determined, the technical description of the 
species will be given. In the meantime the photographs will 
enable any one to identify the new species. There are probably a 
number of new species of Xanthium still undescribed in America, 
as would be indicated by the fact that half of the 8 species now 
recorded for the eastern half of the United States have been known 
less than sixteen years. 
I am indebted to Mr. L. M. PEAcE of the botany department 
of the University of Kansas for the excellent photographs of the 
types, and especially to Dr. J. M. GREENMAN, curator of the her- 
barium of the Missouri Botanical Garden, St. Louis, for examining 
the photographs and comparing the materials with specimens in 
the herbarium, and for information regarding the synonymy of 
X. americanum and X. glabratum with X. canadense Miller. 
UNIVERSITY OF KANSAS 
LAWRENCE, KANSAS 
