Permeability and Defense

Looking at the water gathering on the surface of this holly leaf reminds me that plants are constructed in a strange combination of permeability and impermeability.

Because so much of their metabolism depends on water (and they give off water during photosynthesis), plants have evolved to maintain their water balance in a precise way. They can’t afford to lose too much water during the photosynthetic process or they’ll die.

People have written volumes about the anatomical strategies of plants for maintaining water, and I teach all of this in my courses at Boston University and the Boston Architectural College. Leaf construction, surface hairs, stomata, all very interesting and no doubt I’ll take these topics up in one form or another as we move forward.

But to my knowledge the crucial contradiction in plant form, the fact that plants are so intimately linked to their environment yet so selective about how they interact with their environment, has not been studied in great detail.

Yet as we look at plants and come to appreciate them more we see that every aspect of plant anatomy, from photosynthetic leaves and stems to anthers gently waving in the wind, all have evolved to take advantage of the environment while protecting the plant from potential harm that certainly lurks in that environment.