PERSONALITY OF PLANTS 
it is easy enough for them to thrust their blos- 
soms up into the air, where they may be as dry 
as though they were on land. The sub-aqueous 
plants have a harder problem and are some- 
times driven to developing their flowers in leaf 
air-chambers below the surface. The Water 
Chestnut (Trapa Natans) makes itself buoy- 
ant at its flowering period with generated air 
and rises en masse to the surface. After fertili- 
zation, it sinks again to its sub-aqueous quiet. 
Self-fertilization in its strictest sense occurs 
within the individual flower. Plants only re- 
sort to it as an extreme measure and commonly 
make use of many devices to prevent it. In 
the Iris, the petal-like stamens are in direct 
contact with the pistil and yet self-fertilization 
does not result, because the pollen surface is 
always carefully turned away from the ovary. 
By bringing their pistils and stamens to ma- 
turity at different times, many flowers make 
sure that they will not fertilize themselves. 
Such is the case in the Bulbous Buttercup and 
the Arrowhead. 
Flowers of the same tree or bush might be 
called distant cousins. Their union results in 
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