My first-grader great-grandson Noah is writing a book. The title is "Autumn," and the first page announces that "Autumn has vary old leaves." This sentiment is suitably illustrated, and makes me anxious to see what is to come whenever the mood for page 2 strikes him.
I think this is a wonderfully evocative statement, and the least I can do is to expand on the topic while I wait for more from Noah.
The leaves of autumn are certainly very old, and every day the drifts under the trees grow larger and the sunlight shines through bare branches and glitters on the yellow, orange, red and brown heaped on the ground.
Fun for children, a nuisance to street cleaners, work for homeowners, fodder for compost makers, collection material for Science 101, artifacts for the flower arranger, a delight to the discriminating eye, but what are they really?
My dictionary tells me a leaf is "a usually green, flattened structure of vascular plants, characteristically consisting of a bladelike expansion attached to a stem, and functioning as principal organ of transpiration and photosynthesis." Any botany reference book will go much further and include such terms as chlorophyll, stomata, chloroplast, petiole and lamina.
Most plants do have leaves, in unimaginable variety, but for now let's limit this to tree leaves, as that is what Noah has on his mind.
Each leaf on a tree works to convert the energy of the sun, the carbon dioxide in the air and the minerals and water of the earth into carbohydrates, food for the plant. This process of photosynthesis happens as sunlight shines through the top surface of the leaf and is trapped in the chloroplasts below.
Here, the light energy is changed into chemical energy and is used to convert carbon dioxide from the air into sugar. Tubes in the tree then carry this sugar to the roots, branches and fruits.
Leaves have three main parts: the lamina or leaf blade, which is the wide part, a base at the point where it joins the stem, and a stalk or petiole that connects one to the other. The lamina is the most noticeable part, and this is one important feature for tree identification in most months of the year.
Leaves come in many shapes - simple, which has a single leaf shape, or compound, which has more than one blade. In both types there is a single leaf stem attached to a twig. They are arranged on the stem either alternately, where they are staggered, or opposite, where they are directly across from one another. The edge of the leaf may be entire, lobed or toothed.
While evergreen trees keep individual needles or leaf structures for two or three years, deciduous trees produce new leaves in the spring and hold onto them through the summer until the green coloration disappears, and the basic yellow or orange of the leaf is revealed.
The beautiful red color some species show is anthyocin, which adds so much beauty to the fall display.
As the days get shorter, the tree does not receive enough sunlight for photosynthesis and so it shuts down production and allows the leaves to die and drop.
So there we have it, Noah. Those beautiful autumn leaves have lived useful lives, and once they have completed their work, they fall and eventually decompose into the earth to nourish the ground and bring life to a new generation of leaves.
Ready for page 2?