An event or characteristic, e.g., in evolution or geologic history, that causes or controls a proximate factor.
2.
Ultisols
Soils that are low in bases (less than 35 percent base saturation) in argillic subsurface horizons and to considerable depths. Normally, bases are removed by leaching faster than bases are released by weathering.
3.
ULV
Ultra-Low Volume.
4.
Umbel
Inflorescence in which the peduncles or pedicels of a cluster spring from the same point, as in carrot, coriander, or parsnip.
5.
Umbel
A type of inflorescence in which the minute flower units are arranged into flat or umbrella-shaped heads as in carrots and celery.
6.
Umbric horizon
A thick dark-colored surface horizon (epipedon) similar to a mollic horizon but with low base saturation and may be highly H saturated.
7.
Uncertainty decisions
Decision situations in which no past experiences or historical data are available. Any one of a number of criteria are employed depending upon the personality of the manager.
8.
Underplant
To plant flowers or bulbs beneath the canopy of a larger plant to add color to the garden without taking up additional space.
9.
Understory
Herbs and shrubs that grow beneath a forest canopy.
10.
Ungerminated seeds
Seeds which have not germinated by the end of the test period when tested under the conditions given in rules.
