Leaves arrange themselves to meet the sun

June 16: a perfect day!  It’s one of those startling June days that I want to go on forever.  In fact, when I think of gardening, I think of days like this and forget how infrequent they are.  Yesterday, I felt dull and awkward -- just like the weather.  Today, I am full of zest and ambition -- just like the weather.  The mirror image of mood and weather is sometimes exhilarating, sometimes an annoying inconvenience.

While I spent the past week in a weather funk, the garden just kept on growing.  Zinnias still do battle with bugs, but they’ve turned a corner and seem more robust.  Snapdragons have grown tall.  Plants destined to produce white flowers now equal the height of the faster-paced yellow-flowered snaps.  Foliage is lush and dark green stalks are strong and straight.  

Leaning over the snaps, now almost two feet tall, I study how the leaves grow along the stem.  In the plant world, leaves sprout from stems in several different patterns.  For instance, at each growth-node, leaves can sprout at the same height but on opposite sides of a stalk.  Or leaves can grow in a whorl that completely surrounds a stem. 
Or leaves can occur at regular intervals along a stem but stagger their growth at each node by rotating a quarter turn.  Leaves of my snapdragons grow in this stagger-step pattern.

No matter the pattern of leaf growth, all plants want to reveal as much upper leaf face as possible to the sun.  Since photosynthesis occurs on these top surfaces, plants avoid growth patterns where leaves cast shadows on other leaves.