Michael Bradley, aged 12, Pismo, Calif.,  for his questions:

 Why does moss always row on the north side of a tree?

Can you imagine 14000 different kinds of roses` Of course not. We should run out of colors, shapes and different places to grow them along before we had reached that number. But there are almost 14000 different kinds of mosses. There are varieties of moss just about all over the world. They reach from Greerland’s chill mountains to the frozen continent over the south pole. There are varieties of moss in the hot dry desert of Arizona. Some mosses choose to grow in cool streams, others in hot springs. Some cling to barren rocks. Others carpet the woods and clutch to old lags and tree trunks.

There is hardly a place in the world where some kind of moss could not grow ‑ except iri the salty sea. Most mosses, to be sure, love damp and shady homes. Right now you can find them‑thriving in the winter woods. The forest floor may be covered with snow and fallen leaves. Move the snow and lift up the resting leaves. Chances are, you will find a patch of vibrant green moss thriving in the moist shade below.

Most moss plants do their best in the shade. They need moisture. They can take in water through their leaves directly from the air. Sunny patches tend to dry them out. So we can expect many mosses tc hide from the rays of direct sunlight. In a thick forest, the sunlight may never fall directly on the ground. It is blocked by the spreading branches and thick foliage above. Such forest floors are carpeted with thick mosses. The velvety plants enfold the feet of the tall trees on all sides.

In sparser woods, the sunlight flickers between branches and tree trunks. The shadows of the tree trunks follow the journey of the sun over the sky. The shadow, of course, points away from the shining sun. The south side of the tree is the sunniest. The north side is almost sheltered in shade. If the mosses here are shade‑loving mosses, we can expect the healthiest plants to be on the north, or shady aide of the tree.

But it would not be safe to take our bearings from the moss on one tree trunk. We might be looking at a moss plant that enjoys a little sunlight, or at any rate one tough enough to take it.

Lens look around and stiz1y the mossy situation of twenty, fifty, a hundred trees. Then maybe we can make a guess about the north direction. Even so, it may not be safe to set out for home on this information alone. However, we should discover one thing from our investigation. Mosses do not grow only on the north side of the trees. If we search, we can find these brave little plants growing almost anywhere.