AN INTERESTING MODIFICATION IN XANTHIUM 
43 
and self-fertilized strains is thus precluded so far as this local ap- 
pearance of the variety is concerned. From two other sources have 
come vague reports of the same varieties in other localities, but in- 
vestigation has failed to uncover them. However, it is possible that 
intelligent observation by field botanists might lead to their re- 
discovery. 
Nothing is known regarding the cause, or manner of origin, of the 
glohuliforme type. The character of the modification is such that it 
could hardly result from hybridization, although splitting was noted in 
the 1910 generation. The cause of the sterility is merely conjectural 
and might be due to various factors. Sterility of pollen, if it really 
occurs, would not necessarily indicate a case of hybridization. 
It seems more reasonable to consider it a mutation from X. cana- 
dense Miller. Whether it is progressive, a new condition, or retro- 
gressing toward remote ancestry, one cannot tell. But in view of Farr's 
recent studies on the origin of inflorescences and dicliny in Xanthium,^ 
the latter possibility is particularly significant. Farr reaches the con- 
clusion that the bur is a reduced capitulum, in which the florets now, 
of course, are reduced to two. If this globuliforme type is a reversional 
mutation, it gives a concrete idea of the kind of capitulum from which 
the reduction has occurred. Such a concrete picture is a distinct 
advantage in any attempt to depict the lines along which such an 
evolutionary advance has proceeded. 
The University of Kansas, 
Lawrence, Kansas 
^ Farr, Clifford H., The Origin of the Inflorescences of Xanthium. Bot. Gaz. 
59: 136-148. 1915. 
