We mammals tend to regard plants as stationary objects, inert beings that form a backdrop for the more exciting lives of those us of driven by heartbeats and nerves. Here’s some data from a twig on the sugar maple in my backyard that might call us to a more expansive view of our botanical cousins. The graph shows how the diameter of a growing twig changes over a week.
This is the pulse of the tree: one heartbeat every twenty four hours. The twig is fattest at dawn, then the twig shrinks as the water-conducting vessels, the xylem “tubes,” get pulled inward by the draw of passing water. Like a straw that collapses inward under the influence of an enthusiastic drinker, the twig shrinks and reaches its narrowest point in the early afternoon when the leaves are hemorrhaging water to the hot, thirsty sunshine. The twig then gradually swells as the sun lowers and darkness comes. The movement is slight, a few hundredths of a millimeter each day.
Note that the graph shows an upward trend. This young green twig is adding wood, growing day by day.
All around us: every twig throbbing with life.