He called it "Leaves of Grass."

VOA: special.2009.04.12

Well enough, I guess, of that; although if you want to understand the optimism of that time just dip into Leaves of Grass, read Whitman's Old Pioneers.

我猜这足以驱使他写出这样的作品,但如果你想了解那个时代的乐观主义,只需去翻阅《草叶集》,读读惠特曼的《啊,拓荒者》吧

耶鲁公开课 - 美国内战与重建课程节选

It is the color of grass and the leaves on trees.

VOA: special.2010.05.23