The advancement into new areas by Heterotheca latifolia throughout much of the Georgia Piedmont coincides generally with the combined velocities of all the winds along the directions of the prevailing wind patterns. Camphor-weed does not occur in the mountains partly because the winds have not carried it there as rapidly as winds have moved it into the south and southeast. 2. Within the habitat the achenes generally fall within 30 m. of the parent plant, and most of them fall within 15 m. Wind gusts greater than 12-14 miles per hour and turbulent updrafts carry some seeds aloft, however. Dissemination occurs best on clear days that are abnormally windy and dry, that is, with winds of more than 12 miles per hour and a VPD greater than 10 mm. Hg. 3. The daytime weather at Athens, Georgia, and Spartanburg, South Carolina, is quite similar, except for the direction of the wind patterns. Specific weather data associated with seed dispersal have been summarized for this autumnal season. Early afternoon weather conditions play the most important role in conditioning the plant for dissemination, and turbulent air currents appear to be the principal agents for getting the achenes up and into the path of the moving air mass. 4. An area of 194 plants produced an estimated 3.6 million fruits of which about one-third were accounted for over an area just eight times greater than that occupied by the parent colony.
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Plummer et al. (1963) studied this question.