1915] SHULL—XANTHIUM 475 
to differ (fig. 4). The type with globose burs has much shorter 
seeds than the other two types, which are evidently more closely 
related. The seeds from type I have a dark brown testa, while 
those of type II have a dull greenish or grayish brown testa, and 
type III a yellowish brown testa. 
Fic. 1.—Type I, Xanthium globosum Shull, sp. nov.; natural size 
The variation in size and weight of the seeds of the several types 
is under investigation. The average weight of 50 upper seeds of 
type I in the crop of 1913, an excessively dry year, is about 20 mg., 
of the lowers 27 mg. The corresponding average weights for type 
II are 28 mg. and 48 mg. respectively. The curves of variability 
in weight and length will probably show some overlapping in the 
