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First Page

77

Last Page

96

Abstract

Because of the important role wind is alleged to have in dispersal of fruits and seeds in desert plants, diaspores were collected for experimental study of 14 species from two Sonoran Desert localities of Imperial Co., California. Field observations on natural dispersal of these species also were made. Although all 14 species were not judged to be primarily adapted to anemochory, tests on air transport capability were made using a calibrated and modified seed-blowing machine. Diaspores were tested individually and results for 20 trials averaged for each experimental condition. In one series of tests, lofting ability was determined. In other tests, a Plexiglas wind tunnel was used; the bottom of the tunnel was lined with Plexiglas, wood, and sand for three types of trials respectively. Mean surface area and mean mass were determined for the seeds and fruits ofthe 14 species. These figures and the ratio between surface area and mass were compared to results from the lofting and horizontal movement tests. A high presentation surface area/mass ratio was positively correlated with ease of horizontal movement (tumbling chiefly) and ease of lofting. Excellence at transport in air appears variously countered in the anemochorous species by diaspore characteristics which seem to insure lodging in crevices or depressions. More than one kind of transport in air (e.g., tumbling, floating, skidding) can be identified and particular species may exhibit these in varying proportions. Seeds with high mass have nil wind-dispersal ability and thereby may be adapted to reaching (and staying in) depressions, washes, etc. High static friction is another mechanism which maximizes lodging ability. As Asteraceae show, anemochorous ability does not always run counter to lodging ability: capability of a diaspore to attach to hairs or skin of animals runs parallel to ability to lodge in soil crevices. In the study areas and in other desert localities, ants may play some role in movement of many kinds of seeds and fruits over short distances, but destruction by ants often is excessive.

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© 1985 Jay C. Maddox, Sherwin Carlquist,

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