128 
IOWA ACADEMY OF SCIENCE 
likely to account for the complete sterility of a vigorous plant 
which flowered profusely. 
The stem leaves were quite large, 2 dm. long and 1.5 dm. wide, 
and were distinctly different from either of the supposed par- 
ents, though intermediate between them in a general way. (Plate 
XXI). Long petioles without margins carried triangular blades 
which were palmately 3 — divided with segments somewhat pin- 
natified, the central one distinctly so (PL XXI, fig. 1). From 
another point of view the leaf might be looked upon as a pin- 
nate leaf with greatly enlarged and opposite basilar segments, 
remotely suggestive of Ambrosia artemisiifolia. There is less 
difference than in this species between the stem leaves and those 
of the inflorescenses, the latter being somewhat simpler and 
considerably smaller. The leaf surface was flnely , puberulent 
on both sides, the lower surface being slightly paler in color. 
The leaves, and in fact the whole plant, differed strongly from 
Ambrosia psilostachya DC. 
Flowers were developed abundantly and in the usual rela- 
tion with long spikes of staminate heads above and the short 
stalked pistillate flowers in the axils below. The pollen looked 
normal and the stigmas of the pistillate flowers emerged in the 
usual fashion. Unfortunately no visit was made to the plant at 
a time favorable for securing collections of flowers suited for 
critical morphological study. The only sections obtained were 
those of mature staminate flowers; these showed an abundance 
of seemingly normal pollen though there was no opportunity to 
determine its capacity for germination at the time the collec- 
tions were made. As the plant entered into decline in the early 
autumn it was uprooted and portions preserved. A careful 
examination was made of every pistillate flower but not one 
seed was found. 
The close proximity of several specimens of both the com- 
mon species of ragweed, Ambrosia artemisiifolia and ambrosia 
trifida, suggests that the plant was infertile not only with its 
own pollen but also with that from either of the supposed 
parent species. Some of these plants stood within two feet of 
it, and there would be the fullest opportunity for pollen trans- 
fer from plant to plant. While this sterility has interrupted an 
interesting experiment it may be' that it has inhibited a new 
weed — for this plant looked like one that would make a place 
for itself on Iowa soil. 
Botanical Laboratory, 
State University of Iowa. 
