144 BOTANICAL GAZETTE ‘ [FEBRUARY 
the pistillate flower, is a direct consequence of crowded conditions 
during growth. 
The differences between the staminate and pistillate flowers with 
respect to their protection, vascular supply, and number per 
inflorescence have been variously interpreted. They have been 
considered either as secondary sexual characters, or as a direct 
consequence of the difference in sexuality. In the former case the 
characters associated with the pistillate inflorescence would be 
thought of as having no essential relation to the nature or function 
of the female sex. In the second case it would be held that the 
pistillate flower is protected because it is in need of protection. It 
is apparent that my interpretation follows neither the incidental 
nor the teleological views above named, but ascribes to the char- 
acters associated with each kind of flower a réle of primary impor- 
tance in effecting the transition from hermaphroditism to dicliny. 
In other words, many of the differences between pistillate and 
staminate flowers appeared while the flowers were still perfect; 
and the effects of their presence occasioned the abortion of pistils 
and stamens respectively, resulting in the dicliny of this species. 
Ambrosia and Franseria resemble Xanthium not only in their 
type of dicliny, but also in the peculiar burlike female inflorescence, 
the principal difference being that they have but one flower in each 
pistillate capitulum. Although there is need of further investi- 
gation, it may be well at this time to note what relation these genera 
bear to the conclusions reached above. RostowzEw (13) stated 
that the pistillate heads of both forms are found in the axils of 
leaves. Furthermore, GoEBEL (9), in referring to Ambrosia, said, 
“In no instance have I observed in the male capitula even a trace 
of a subtending bract.” The vascular supply has been studied 
only in the peduncle of the staminate head of Ambrosia, in which 
the last named writer found only two or three bundles. It is a 
matter of common knowledge that in both these genera staminate 
heads are terminal and peduncled, while pistillate are axillary and 
sessile. Evidently, therefore, Ambrosia and Franseria agree 
closely with the conditions in Xanthium as regards the position, 
protection, and, so far as known, the vascular supply of the heads. 
Thus it seems likely that the foregoing interpretation of the origin 
