イロハモミジの翼果 (The Samaras of Japanese Maple)

　イロハモミジ（カエデ科）。2011年5月8日、鈴の宮公園で。

　2009年に同じく鈴の宮公園で撮影したこの植物の翼果の写真を掲載した少しあとに、オランダとアメリカの科学者たちが、カエデとシデの種子が飛ぶ様子を風洞実験で観測した（厳密にいえば、種子は翼果の中心部分に収まっており、翼果の模型と実物を使って実験したのである）ことについての論文を Sience 誌に発表した [1]。そこで、「後日の追記」として、その結論を、「種子の落下中にその各翼の上部に空気の安定な渦ができ、それが浮力を生じて種子を長い時間空気中に浮かせる原因になっていることを見出した」と、簡単に紹介した。今回は、その論文のアブストラクトを英文のまま注欄に引用しておく。

Japanese maple; botanical name Acer palmatum; family, Aceraceae. The photo was taken in Suzunomiya Park, on May 8, 2011.

A little after I posted a similar photo of the samaras of this plant in 2009, scientists of the Netherlands and USA published a paper on the wind-tunnel observation of flying maple and hornbeam seeds in Science [1]. So, I added a note briefly to introduce their conclusion that the seeds attain high lift by generating a stable leading-edge vortex as they descend. This time, I quote the abstract of their paper below.

1. D. Lentink1, W. B. Dickson, J. L. van Leeuwen and M. H. Dickinson, "Leading-edge vortices elevate lift of autorotating plant seeds." Science Vol. 324, No. 5933 pp. 1438–1440 (2009) (DOI: 10.1126/science.1174196).
   Abstract: As they descend, the autorotating seeds of maples and some other trees generate unexpectedly high lift, but how they attain this elevated performance is unknown. To elucidate the mechanisms responsible, we measured the three-dimensional flow around dynamically scaled models of maple and hornbeam seeds. Our results indicate that these seeds attain high lift by generating a stable leading-edge vortex (LEV) as they descend. The compact LEV, which we verified on real specimens, allows maple seeds to remain in the air more effectively than do a variety of nonautorotating seeds. LEVs also explain the high lift generated by hovering insects, bats, and possibly birds, suggesting that the use of LEVs represents a convergent aerodynamic solution in the evolution of flight performance in both animals and plants.