葉，為什麼薄而堅韌？京都大學解釋結構

A few weeks ago the Asahi News on-line reported the following:

葉っぱ、薄いのになぜ丈夫？　京大が構造を解明

阿部彰芳

2015年2月14日09時46分

　植物の葉っぱは薄いのになぜ丈夫なのか？　その理由は、飛行機の翼などと同じ構造にあることを、京都大などのグループが確かめた。英専門誌に１２日発表した。

　地上に生い茂っている植物の葉は、表皮が内部組織（葉肉）を挟み込む構造になっているが、二つの堅さの違いは不明だった。

　京大の小野田雄介助教（植物生態学）らは、葉に力を加えた際の弾力を元に表皮や葉肉の堅さを測る手法を考案。シロイヌナズナやアオキなど３６種類の草木を調べたところ、どの葉も表皮より葉肉の方が柔らかいことがわかった。表皮は、アサガオなど落葉する草と比べ、ツバキなどの常緑樹が約５倍堅かった。

　堅い表面が柔らかい内部を挟む構造は「サンドイッチ構造」と呼ばれる。効率的に強度を高められるため、飛行機の翼など先端工学にも使われている。

　小野田さんは「植物にとって、軽量で葉の面積を広げる最適な構造。新素材の開発にも応用できるのではないか」と話している。（阿部彰芳）

(試譯文)

Why the leaf of vegetation although thin was strong? A group from the Kyoto University confirmed that it was for a reason that an airplane’s wing was using the same structure. It was announced in a British specialized magazine on the 12th (February).

The leaf of vegetation had a widespread growth on the ground; regarding the epidermis which was wrapping the internal structural organization (mesophyll), the difference in firmness of the two was unclear.

  Onoda Yusuke the assistant professor (Plant ecology) and others of the Kyoto University contrived a method to measure both the firmness of the epidermis and the mesophyll based on their elasticity when a force was applied to them. Arabidopsis and Japanese laurel etc. 36 kinds of vegetation were checked to find out in what leaf the mesophyll was softer than the epidermis. For the epidermis, compared to the deciduous grass such as morning glory, the evergreen plants such as camellia was about five times stiffer.

  The firm surface structure surrounding the soft interior was called "sandwiched structure". The wing of an airplane etc. advanced engineering were also using this structure because strength could be raised effectively.

  Mr. Onoda was saying that “for a plant, the most suitable structure in leaf is to have large surface area yet light-weight; may be it can also be applied to the development of new materials".

It is an interesting finding that could help the design in building materials etc.