Ken Watson, age 12, of Niagara Falls, Ont., Can., for his question:

WHAT WERE THE FIRST TREES LIKE?

There were vast forests on the earth long before the first trees arrived. Actually they were crowded with giant ferns, huge scrawny horsetails and other strange vegetation. Some of those huge plants grew as high or higher than 40 feet. But they had no woody trunks, and they produced no real seeds. So they did not qualify as genuine trees.

The story of the plant world goes back more than 3 billion years, when single celled algae thrived in the ancient freshwater seas. Simple land dwelling plants arrived perhaps half a billion years ago. There they grew bigger, more elaborate and more varied. Around 400 million years ago, tree size ferns and horsetails grew in vast forests that later formed beds of coal.

Some of those giants of the coal forest had hollow trunks, and others had stems like rolls of paper. Most of them produced zillions of dusty spores, and only a few of these tiny seedlets survived. Then, perhaps 300 million years ago, the first genuine trees arrived. They had woody trunks and produced well developed seeds. Most of these splendid plants were so successful that no improvements were needed.

Most likely the world's first real trees looked like Christmas trees. They were the ancestors of our furry green pines and other cone bearing trees. Their seeds were the first real seeds of the plant world. These trees were patient parents, male and female.

The smaller male cones developed clouds of windblown pollen, which fertilized the cells in the female cones. There the seeds developed until they were ready to fall to the ground. Many of the first trees were evergreens, able to cope with changing seasons. They succeeded and spread to cover much of the earth with evergreen forests.

Another early tree was the ginkgo, or the maidenhair fern tree. Its dainty fan shape leaves were shed in the fall, and ages ago there were huge ginkgo forests in North America.

Later, most of them died out.  The few that survived were pampered in China, where the ginkgo was regarded as a sacred tree.

For perhaps 150 million years, the conifers were the world's most advanced plants. Then a wondrous assortment of flowering plants arrived. A flower may produce both male and female cells. The seeds have superior protection and a better chance to survive.