Plants Are Metropolises. Organic, Green Metropolises.

It's no mystery that in terms of overall structure, what separates plant cells from the cells of other organisms is the cell wall. Knowing that, it's also no mystery that those walls play huge parts in plant cell function and differentiation. Such is so for the 'chyma cells. While parenchymas happen to be the seeming structurally blandest and yet the most functionally flexible with their thin primary walls and lack of secondary walls, their smaller counterparts, elongating collenchyma and lignin-secured sclerenchyma have thick cell walls perfect for their rolls as support cells. The other half of the spectrum belongs to cells that are essentially advanced delivery shoots. Thick-walled tracheids and vessels are tubes that are dead at maturity, and use "end walls" to transport water. Their cousins, or whatever you'd call them, ribosome and nucleus-lacking sieve-tubes, use similar "end walls" to transport various nutrients such as sugar. Just imagine what life would be like if our cities cleaned themselves, protected themselves, repaired themselves, and transported materials themselves like plants do.