The Survival of Green Things
Just about everyone is thinking spring these days. The early spring flowers are beginning to add color to winter's drab landscape. Trees are budding and many other things are beginning to grow. Plants are usually pretty dedicated survivors, you have to admire them. Think about it, they grow and reproduce themselves and live their whole lives in the same patch of earth. You have to be creative to get everything you need without ever moving around. Plants achieved this with seeds.
It may surprise you to know that plants weren't always on land, in fact, they evolved in Earth's oceans. Then about 450 million years ago, plants began taking advantage of the opportunities of land. But to do this, plants needed to change, they needed to develop roots, leaves with pores to take in moisture and most importantly, plants needed a way of successfully reproducing on land. That's where seeds come into the picture.. The first seeds we know are at least 360 million years old. The emergence of seeds allowed plants to do a full scale invasion of land, and plants continued to evolve incredibly well to adapt to nearly every spot on the Earth!
There are a couple of reasons why plants needed seeds. The seed encases the baby plant, keeping it safe from too much or too little moisture. It also helps protect it from too much heat or cold. The seed also contains nutrients which sustain the baby plant until it can grow and feed itself through photosynthesis. This stored food helps the embryo grow in the early stages of its development -- so it increases the young plant's chance of survival because it might be awhile until the plant is able to sprout.
The next challenge for plants was to spread its seeds around. If all the seeds fell right beneath the parent plant, it would be much harder to survive with all the competition for space and nutrients from the bigger plant's roots. Also, if all the seeds were in the same spot, they could all be killed if say a puddle formed over them and they rotted. The best chance for the most seeds to survive was to spread them around. And spreading seeds around is exactly what plants got good at in a number of ways.
In some ways it seemed plants were real opportunists. They developed flowers which attracted birds and insects. This achieved pollination without any movement on the plants part, which was clearly impossible. To spread the seeds, some plants the contained its seeds within a fruit, the fruit is useful in attracting birds, mammals, and insects, all of which help spread seeds around. Other plants developed seeds with "wings" like those of maple trees. These wings help air currents lift the seeds and carry them sometimes great distances. Other plants developed "stickers" which would cling to passing animals and hitch rides to other parts. One way or another, plants got around!
In spite of all this seedy creativity there are many "seedless" plants alive today, including ferns and horsetails - found in damp environments - as well as many aquatic plants. These plants have found other ways, some by root extensions, to multiply. But seeds are still the most popular offense of the great plant invasion.
Copyright © 1999 Kathy Miles and Charles F. Peters II