The mystique of fossils and leaves

While in-between appointments recently in the big city, I ventured outside to investigate a dry creek bed.

Even with subtle lighting, handsome art prints and sometimes-interesting reading, waiting rooms are not very inviting. In this case, wall-to-wall windows with open blinds drew me outside.

The creek was only steps away from the multi-story building. Many rocks had been deposited by crews into the basin to manage water flow as part of the overall flood-management plan, but the mostly barren banks were fairly unaltered by people. 

I walked over for a closer look. I crouched down, drawn to the small limestone pieces and abundant pebble-litter just beneath the surface.  An army of ants let me know promptly that I was in their camp, so I moved over about 5 feet. 

Poking just below the surface with a rock, I unearthed some intriguing quarter-size fossils, remnants of an ancient sea. I got really excited when I dug up a small fossilized tooth. 

I looked to the skies to reflect on the time when the animals that became the fossils were still alive. As I glanced up, a mockingbird perched in a live oak tree serenaded me. It was as if he was begging for an audience to hear his new fall-winter song. I got up and walked over to acknowledge his sweet voice; he sang and sang.

With the concert concluded, I wandered about examining the native and adaptive plants that had survived around the creek bed.  

Then there were the leaves. For whatever reason, I am and always have been amazed by leaves.  

Many already littered the ground. Others were getting ready for their winter slumber. Some, like the flameleaf sumac, were tinted with all the colors of fall.

I always wanted to press leaves but never have. They are so exuberantly diverse in size and shape as to defy explanation if not description.

They can be shaped like hearts, pinwheels, arrowheads and fans; they can be soft and smooth like lamb’s ear or rough and prickly like agarita. 

They can be bald or hairy. They can be large like elephant ears or tiny like some wildflowers. Some, where water is abundant, have pointy ends which serve to draw water off. Undoubtedly, they are shaped accordingly because of their evolution.

Each is designed to capture light in order to maximize photosynthesis, the fundamental process by which plants combine minerals and water from soil, carbon dioxide from air, a green pigment called chlorophyll and sunlight to produce carbohydrates, such as sugar, and oxygen for growth. 

In the tropics, leaves generally tend to be big and broad because there is plenty of water, lots of competition for sunlight and the weather is relatively mild. In colder and drier climates, leaves tend to be smaller, narrower and thicker.

The boundary layer, the zone where air rubs up against the leaf surface, also affects leaf shape. For plants in full sun, a thick boundary layer is important, insulating leaves from heat and moisture loss. 

Many plants boost their efficiency by growing hairs that trap even more air and moisture, further cooling the plant. Some plants simply reduce leaf size and corresponding boundary layers. Smaller leaflets, like those found on maples and oaks, produce the same effect.

Soil quality also affects leaf shape. In nitrogen-rich soil, plants can make big, nitrogen-packed leaves capable of a high rate of photosynthesis. 

In nitrogen-poor soils, the rate of photosynthesis is necessarily slower and leaves must remain on the plant longer.

I wandered about the grounds, touching, thinking and wondering as I waited for my next appointment. Eventually, I stepped back into the building and entered the other world. 

I’ll be back to catch all the color as the days cool.

Delgado and Scott are members of the Highland Lakes Birding and Wildflower Society, the Texas Archaeological Society and the National Audubon Society. E-mail them at viva.dana@yahoo.com