Hank gets into the dirty details about vascular plant reproduction: they use the basic alternation of generations developed by nonvascular plants 470 million years ago, but they've tricked it out so that it works a whole lot differently compared to the way it did back in the Ordovician swamps where it got its start. Here's how the vascular plants (ferns, gymnosperms and angiosperms) do it. [10:24]