If you live in a place like Michigan where we live, you may tend to
take the leaves on the plants around you for granted. We all know
about the work leaves present to us in the fall, and are aware that
they sustain plants. The fact is that leaves have some amazing
engineering, and do many things that most of us are not aware of.
All leaves have what is called a cuticle, a waxy coating on their surfaces that in land plants is vital to survival. In tall trees especially, the leaves are dotted with microscopic mouth-shaped openings which are surrounded by guard cells. When the plant is low on water, these cells soften and close the openings to retain water. When the plant has plenty of water, these cells stiffen and open the structures which allows evaporation. This process allows the exchange of oxygen and carbon dioxide that sustains all life on earth.
Leaves have specialized purposes in different plants. In a cactus the leaf-like surfaces contract and expand like an accordion to allow the maximum storage of water. In many plants leaves roll up as wind velocity increases. When the wind velocity is very high the leaves make a cone minimizing the affect of the wind on the tree. Leaves also are shaped like a weather vane so they reduce the drag of wind and minimize the possibility of the wind breaking the limb or tearing the leaf off the tree.
When winter approaches the trees stop producing chlorophyll. The pigments that are left are the carotenoids which have the red and yellow colors we all associate with fall. A hormone in the tree causes the cells at the base of each leaf to seal off the base of the leaf allowing and causing the leaf to fall from the tree without damaging the plant.
One of the things that complicates this picture for evolutionists is the fact that water plants have none of these problems and have no need of most of what we have described here. Evolutionary explanations would require the plants to have produced these characteristics after they became land plants, or would require the adaptations to develop when natural selection would not have been a factor. Leaves testify to the wisdom and design we see in all of nature, and we would suggest they are an eloquent demonstration of the fact that the world in which we live is not a product of chance.
--Our thanks to Chuck Cromwell for the information on this subject.
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