482 BOTANICAL GAZETTE [yoNE 
of breeding test be considered as a species distinct from X. cana- 
dense Miller. 
The burs of type I do not resemble those of any of the 8 species 
now recognized in the territory east of the rooth meridian. This 
variety was first seen on the campus of the State University of 
Kentucky several years ago, where it formed a very small percentage 
of the cocklebur population. But here it was the most prominent 
variety in the field at the time the original selection was made in 
1912. In addition, it is the most prolific type so far found. One 
specimen of average size bore 1864 burs, as compared to 75 on 
X. speciosum. It has been found to breed true, and since it is 
distinguished at once by its short smooth globose bur, I am naming 
it tentatively Xanthium globosum. 
No study has yet been made of the geographical distribution 
and probable migrations of the several forms. The possibility 
suggests itself that X. globosum is a southern or southwestern form, 
developed in a region favorable to a long developmental period, 
and that X. pennsylvanicum is of more northern origin, with a 
correspondingly short period of growth. The two types may have 
met and mingled in the plains region without the possibility of a 
general hybridization because of the physiological isolation. An 
illustration of the behavior of a northern species may be cited in 
this connection. Seeds of X. speciosum Kearney obtained from 
South Dakota were planted about June 1, 1914, and had half grown 
burs by July 20, almost a full month before X. pennsylvanicum 
had developed its flowers, and six weeks before X. globosum was 
in bloom. 
X. canadense Miller, as here interpreted, is in a number of ways 
intermediate between X. globosum and X. pennsylvanicum. It has 
an intermediate blooming period, intermediate sized burs and 
seeds, although the seeds stand much nearer to X. pennsylvanicum 
than to X. globosum, and intermediate production of anthocyanin. 
It has the oblong shape of X. pennsylvanicum, the glabrous char- 
acter of the bur and the somewhat crinkly leaf of X. globosum. It 
is not yet known whether X. canadense can be produced by crossing 
X. globosum and X. pennsylvanicum, and selecting a pure form 
having the recombinations which it shows. While in general the 
