Abstract
In a manipulative experiment the following predictions about the relationship between fruit mass, pappus area, and terminal velocity in the fruits of Tragopogon dubious (L.) were tested: (1) terminal velocity should be proportional to the square root of disk loading (disk loading = mass/area), (2) when pappus area is held constant, terminal velocity should be proportional to the square root of the mass and (3) when fruit mass is held constant, terminal velocity should be inversely proportional to the square root of pappus area. Although qualitative support was found for each prediction, terminal velocity declined more slowly than predicted with increasing pappus area and increased more quickly than expected when mass was increased. When disk loading was held constant, fruits with larger pappuses fell more quickly than fruits with smaller pappuses. These results suggest that the area of the pappus is not a good estimator of its ability to produce drag (its effective area) for two reasons: (1) because the radial morphology of the pappus causes the density of drag producing cross hairs to decrease along the length of the pappus ray and (2) because the projected area of the pappus may change if the pappus is bent upwards by the drag force acting on it. Thus, increasing parental investment in pappuses does not decrease terminal velocity as quickly as expected.
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Claims 7
Claim · model-written summary
The three predicted qualitative relations among disk loading, mass, pappus area and terminal velocity had support.
Not reportedDirection
Verbatim
t0“Fruit Morphology and Terminal Velocity in Tragopogon dubious (L.)”
e0“Although qualitative support was found for each prediction”
Claim · model-written summary
Terminal velocity declined more slowly than predicted as pappus area increased.
Verbatim
t0“Tragopogon dubious (L.)”
e0“terminal velocity declined more slowly than predicted with increasing pappus area”
Claim · model-written summary
Terminal velocity increased more quickly than expected as mass increased.
Verbatim
t0“Fruit Morphology and Terminal Velocity in Tragopogon dubious (L.)”
e0“increased more quickly than expected when mass was increased”
e1“terminal velocity declined more slowly than predicted with increasing pappus area and increased more quickly than expected when mass was increased”
Claim · model-written summary
At constant disk loading, fruits with larger pappuses fell faster than those with smaller pappuses.
Verbatim
t0“Tragopogon dubious (L.)”
e0“When disk loading was held constant, fruits with larger pappuses fell more quickly than fruits with smaller pappuses”
Claim · model-written summary
Pappus area was judged a poor estimator of its effective drag-producing area.
Verbatim
t0“Tragopogon dubious (L.)”
e0“the area of the pappus is not a good estimator of its ability to produce drag (its effective area)”
e1“because the radial morphology of the pappus causes the density of drag producing cross hairs to decrease along the length of the pappus ray”
Claim · model-written summary
Pappus bending under drag may alter its projected area.
Verbatim
t0“Tragopogon dubious (L.)”
e0“the projected area of the pappus may change if the pappus is bent upwards by the drag force acting on it”
Claim · model-written summary
Greater parental investment in pappuses reduces terminal velocity less quickly than expected.
Verbatim
t0“Tragopogon dubious (L.)”
e0“increasing parental investment in pappuses does not decrease terminal velocity as quickly as expected”