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IOWA ACADEMY OF SCIENCE 
these plants quite carefully in the Okoboji region and was impi :ii.teed by the 
uniform flowering habits of the plant at varying depths of submergence. It 
was noted that whereas the submerged flowers never open they seemed to set 
seed with perfect regularity. This suggested that the flowers were either 
cleistogamous or that the embryos develop apogamously. 
Numerous dissections of the mature but unopened flowers showed that they 
were self-pollinated. Within the flower bud scores of pollen grains were 
found adhering to the stigma, and with a hand lens the pollen tubes could be 
seen entering its tissues. Further study of these unopen flowers showed that 
all the pollen in the anther germinates even though but the tip of the stamen 
comes in contact with the stigmatic hairs. With forceps the whole pollen-mass, 
consisting of spores and tangled pollen tubes, could be lifted from the anther 
as a mass. Most of these tubes never reach the stigma but turn and twist in 
various ways within the anther. Obviously the stimulus to germination is 
transmitted from the stigma throughout the pollen-mass and to spores that lie 
even at the opposite end of the pollen-sack. 
An abundance of material was collected for more careful study and details 
may be expected in a later paper. A preliminary study of the sections shows, 
however, that the pollen tubes reach the ovules so there is no reason for sus- 
pecting apogamy. 
In this connection it may be recalled that clesitogamy is apparently rare 
among submerged seed-plants, where, on account of the difficulties in the way 
of cross-pollination one might expect to find it of common occurrence. On the 
other hand, there seems among many forms a pronounced tendency away from 
the bisporangiate to the monosporangiate type of flower. It would appear that 
the general tendency toward dioecism in so many of the submersed aquatics 
might be to avoid self-pollination. 
