What's that look like? Perhaps I spend too much time staring at cities in google earth delving into a trance-like state and a world of mental abstractia...
Medieval core of Bologna
Medieval Core of Valencia
What do these have in common with the leaf? They were developed by forced intelligence. A leaf has no room to spare for luxury. These cities were designed and built during times of scarcity. All decisions were dictated by necessity and efficiency: climate, terrain, practicality of non-intensive energy use, locational and spatial efficiency, trade feasibility (along veins, betwixt and between the cellulosic structured urban foliage) and commercial rationality.
Xylem up, and Phloem down. Amazing the pnemonic devices one remembers from 9th grade biology.
This will be the century where Biology will inform all disciplines for the better.