Donna Deboer, age 11, of Hull, Iowa, for her question:

How does moss go to seed?

A marigold plant bears sunny colored flowers that soon fade away. The petals fall and in their places come tufts of seeds for more marigolds. The simple mosses have no eye catching flowers, but they have a far more complicated way of going to seed than the razzle dazzle marigolds.

The mosses spread like carpets on the moist ground and cling like snug jackets to shady tree trunks. But they have no true plant roots to anchor them to the spot. Their delicate foliage is anchored by rootlets_ called rhizoids. New plants can grow from spreading foliage, or a moss plant may go to seed in a very special way of its own.

A thriving moss plant may grow an extra long tuft of foliage that bends to touch the ground where it develops a new set of rhizoids. It also sprouts two types of leafy tufts, one male and one female. The male branch is called the antheridium and is topped with a small package of sperm cells. The female branch is the archegonium, and at the top of the leafy tuft is an egg cell.

On some dewy morning the ripe sperm cells leave the antheridium and swim along in the misty moisture that films the leafy foliage. Some of them reach and unite with female cells. Each union forms a fertilized cell that takes root on the archtgonium. It grows a thin, leafless stem which is soon topped with a tiny spore case.

The developing spores within the capsule are actually seedlets too small to be called seeds. The tip of the spore capsule is closed with a circle of tiny prongs and sealed with a tiny cap. When the spores are ripe, the cap falls off. The pronged doorway opens and closes with the changing weather. ._,

Mosses need shade and moisture, and their spores have a better chance of finding a suitable home in moist weather. When the woods are wet with rain or dew, the spore capsule opens its pronged door and out come a few ripe seedlets. Each spore that is lucky settles on the ground and sprouts a branch of green threads called a protonema. The protenema sends down the rhizaids and sprouts up the leafy tufts of a new moss plant.

For such a simple plant, the moss has~a very complicated way of going to seed. The method is called alteration of generations, and it takes place in two separate stagfs. Maie and female cells unite to form the fertilized egg from which the spores develop. A spore grows a flat branch of threads which produces the new moss plant