Clouding the Issue

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Science  22 Oct 2010:
Vol. 330, Issue 6003, pp. 429
DOI: 10.1126/science.330.6003.429-a

As anyone who has played table tennis knows, it's hard to throw a table tennis ball very far. Fungal spores, being even smaller and lighter, suffer much more from drag when they are ejected into air; individual Sclerotinia sclerotiorum spores are roughly 10 µm in size and would be predicted to travel only 3 mm after having been launched at a speed of almost 10 m s−1. Streamlining the shape of the spore and sticking to one's brethren do confer some aerodynamic advantages and lead to wider dispersal. Roper et al. show that emerging in a cloud helps, too, and can boost the distance traveled to as much as 10 cm. This enhancement arises from the earliest spores having set the proximal layer of air into motion so that later spores can go with the flow. The authors numerically simulate the spatiotemporal behavior of the spore jet and find a good match with particle-imaging velocimetry measurements. They also find that spores that wait to emerge, so as to board the already moving air mass, can delay their departure only by around 50 ms lest the train leave the station without them.

Proc. Natl. Acad. Sci. U.S.A. 107, 10.1073/pnas.1003577107 (2010).

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