1915] FARR—INFLORESCENCES OF XANTHIUM 137 
and he has been followed in this by many workers, including Batt- 
LON (2) and GorBEL (9). However, KoEHNE (12) as long ago as 
1869 conceived of them as involucral bracts; while HorMANN (6) 
referred to them as ‘“‘Spreublitter’’; and Rostowzew (13) simply 
called them modified bracts. 
These diversities of interpretation have doubtless been due to 
an inadequate knowledge of organogeny, and to an incomplete 
correlation of the spines, bracts, etc., of related genera. A con- 
siderable number of typical Compositae have been investigated 
and the morphology of their parts is well established. The Ambro- 
siaceae, the tribe to which Xanthium belongs, has been excluded 
from the Compositae by some, though several of its genera approach 
very near to the typical form of Compositae. Iva is without doubt 
that member of the Ambrosiaceae most closely resembling these 
Compositae, and a recent discussion of Iva xanthiifolia Nutt. by 
the writer (7) involved the homology of its bracts and rudimentary 
structures with corresponding organs in the inflorescence of the 
typical Compositae. This paper also presented a hypothesis as 
to the origin of dicliny in that species. The present investigation 
was undertaken in the hope that the results of the preceding study 
might aid in the explanation of the dicliny in Xanthium and the 
interpretation of its peculiar pistillate inflorescence. I wish to 
express my appreciation for the encouragement and suggestions 
of Dr. R. B. Wyre under whose supervision the work was pur- 
sued; and thanks are also due to Dr. J. C. ARTHUR for assistance 
in the Serer tin of species. 
The staminate inflorescence 
The species investigated was Xanthium commune Britton, in 
which staminate and pistillate capitula are associated on the same 
branch. The staminate head, which bears 1 50-175 flowers, is often 
solitary and always terminal, thus occupying an exposed position. 
The peduncle (fig. 2) on which it rises above the pistillate heads is 
quite slender in comparison with similar structures. Its length 
nearly always equals or exceeds the diameter of the head which it 
ears; while its own diameter is onlyabout one-sixth as great. Three 
vascular bundles (fig. 4) run throughout the length of the peduncle, 
