After travelling long distances a variety of factors aide the deposition of spores from air. Of the factors that aid deposition, impaction, sedimentation and rain deposit appear to be most important.

Impaction is caused by the spore being too heavy to be carried in the air flow as it passes around an object. Most airborne spores will bypass an immobile object, but a proportion impact on the object. Efficiency of impaction increases with wind speed, increasing mass of spores, small diameter of the object, and by the spore being sticky. Most spores would not impact on a tree trunk, but many plant pathogens have heavy spores that enable impaction on narrower objects such as stems and leaves.

Sedimentation takes place when the air current is too slow to carry the spores. Gravity causes the spores to drop. Usually sedimentation only takes place in the boundary layer, which is normally up to 1mm above a surface. However, on still nights, the boundary layer may be 1m above ground layer....

bugs.bio.usyd.edu.au/learning/...Dispersal/sporeDispersal.shtml

The search linked below (for some reason trying to paste it in the "web references" field results in an error) seems to suggest that floating/falling might be one way to express that distinction, but I'm way out of my field here, so more research/confirmation is advisable.


http://jglobal.jst.go.jp/search.php#{%22keyword%22%3A%22%E6%B5%AE%E9%81%8A%E3%80%80%E8%90%BD%E4%B8%8B%22%2C%22synonym%22%3Anull%2C%22category%22%3A0%2C%22order%22%3A%22score%22%2C%22limit%22%3A20%2C%22page%22%3A1%2C%22words%22%3A[]}

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Note added at 3 days10 hrs (2013-04-01 07:08:36 GMT)
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You will need to copy the whole long URL, right to the last bracket, to get directly to the result. You can also just search for "浮遊　落下" on jglobal if the first method doesn't work.