The deep and extensive roots of sunflowers make them another good candidate for resisting extreme conditions.

VOA: special.2010.02.09

There you have the roots and the kernel of the so-called "Positive good thesis "About slavery.

这样你就有了奴隶制,所谓"积极的一面"的根源和依据

耶鲁公开课 - 美国内战与重建课程节选