154 
IOWA ACADEMY OF SCIENCE 
is quite possible that nectaries may arise in either way, but unless: evi- 
dence to the contrary is shown, it seems better to consider them derived 
structures. These small structures in Iva may therefore be considered 
vestiges of an inner whorl of stamens. 
The development of the pistil of the staminate flower is very different 
from that of the fertile flower. No ovarian cavity is formed, but quite 
early a notch appears in the center of the upper surface of the papilla 
(fig. 3). This notch is later obliterated by the growth of large hairs 
which form a broad capitate disc at: the apex of the mature style. Al- 
though Chamberlain (2) contends that this style “is undivided,” it is 
seen to be somewhat cleft during its development, an indication or 
derivation from the typical bifid form. 
The abortive pistil doubtless aids in the dehiscence of the anthers. 
As the style elongates it pushes against the hook-like tips (“Anhang- 
seln” 4) of the stamens, which arch over its capitate disc, and in this 
way probably tears open the pollen chambers. The capitate structure 
seems to serve a further purp'ose during pollination in preventing the 
microspores from being shed en masse. Wernham (16) believes that in 
the Compositae the style “forces its way through the anther tube, sweep- 
ing the pollen before it. ? ’ That this is not the case in Iva is shown by 
the position of the style prior to dehiscence (fig. 4), the brush hairs 
being above most: of the pollen mass. 
That this structure in the center of the staminate flowers of Iva 
xa,ntliiifoJia } Nutt, is a rudimentary pistil can scarcely be doubted. The 
position, the tardy appearance, the notch, the brush hairs and the stylar 
thrust all point to this interpretation. 
THE PISTILLATE FLOWER. 
The development of the pistillate flower presents only a few pecul- 
iarities. The coralla is abortive, never becoming lobed, and does not 
normally develop to more than one-fifth the length of the mature style 
(fig. 10). In contrast with Silphium (9) the abortive stamens of the 
pistillate flower of Iva appear after the carpels. Furthermore these 
rudimentary stamens are not distinct but form a continuous collar-like 
structure about the base of the style. That this collar is the vestige of 
a whorl of stamens is further indicated by an abnormal flower which 
was found in the material examined. 
ABNORMAL FLOWERS. 
In one of these abnormal pistillate flowers the only irregularity con- 
sisted in the lengthening of the abortive coralla, which was better dev el- 
