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WOOD EVOLUTION

   The diversity of wood when seen with a microscope is so great that one can identify many woods to genus and, not infrequently, even to species.  But what explains this diversity?  Over geological time, woody plants have adapted to distinctive ecological situations—and by multiple pathways.  Conductive efficiency, conductive safety, and mechanical strength are often cited as the main functions of wood, but there are others (storage and conduction of photosynthates, for example).  There are obviously numerous solutions to how these functions are accomplished.  Experiments do answer particular questions about how woods function, so why is comparative anatomy desirable for understanding how wood evolves?
    Obviously, there is more than one solution to each of the functions that wood performs.  My work begins with the assumption that the diverse expressions in wood anatomy are functioning successfully in the environments where plants with those types of wood grow.  When one looks at wood under a microscope, one is looking at a functional design that has a story.  One can avoid trying to understand the story, and just give a description based on terminology.  Avoidance of evolutionary stories is tempting, because they often contain so many concurrent elements and complicated factors.  To understand a wood properly, one must know the growth form of the plant, the year-round ecology of the habitat in which the plant grows, where the plant belongs in a taxonomic system, the phylogenetic ancestry of the plant, and how that particular wood differs from or is similar to woods of related species (and unrelated species in the same habitat).  One must even know whether the wood was from a root or stem, from an old plant or a young one.  Too much to ask?  Clearly, but one can at least see parts of the story of any wood. 
    The wood evolution topics that I include in this section of the website are those parts of a story.  Like parts in a jigsaw puzzle, explanations in science fall into place one piece at a time.  The approaches to wood evolution here use microscopy with the understanding that woods exist in larger contexts.  Comparative anatomy, the method used here, is wonderful for showing correlations between structure and function.  Experiments can show how woods function, but experiments inevitably focus on one feature of wood and use one or a few species to demonstrate how that feature works. Experiments are designed to show phenomena in as clearly as possible, and thus have admirable simplicity. Comparative wood anatomy shows a bigger picture of how evolution works.  The complexities of wood function are evident when one looks at woods with a microscope. 
    Experimental work on how woods function is based on questions.  Where do those questions come from?  Directly or indirectly, they come from understanding of wood anatomy.  Correlating wood anatomy with function, ecology, and evolutionary history can be demeaned as speculative activities.  “Speculation” is a favorite word used by scientists who wish to be dismissive of an idea of another scientist.  The same idea can be viewed as a “good hypothesis” if one is inclined to view that scientist more favorably.  Naturally, I think that the stories of wood evolution presented here are good hypotheses.