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 ====IV. Water Babies that Live on Land==== Did you ever see a tad-pole? A tad-pole is a baby frog, you know, but it looks more like a baby fish. It breathes through feather-like gills. You can keep one in a gold fish bowl and watch it turn into a frog. Behind the gills a pair of little flippers pop out. They grow into legs. Then the gills go inside and become lungs. The hind legs come next. The tail grows shorter, and the animal broader. One day the tad-pole is gone. The frog jumps out on a rock and catches an insect for dinner. He sits blinking in the sun as if he wonders how he did it. The frog is a land animal that grew from a water baby. It likes to live on the edge of a pond where it can dive and swim whenever it feels like it.

There are plants something like that. They were born seaweeds or algae. You remember that some of the algae were so near the surface of the water that they turned green in the sunlight, and became able to make their own food? Many of them were lifted slowly, on rising seacoasts until, at last, they found themselves in the water part of the time, and part of the time out in the air. If these algae were to live, they had to jump from swimming tad-pole seaweeds into—not quite, but almost into froggy mosses with legs, and air-breathing lungs. They became those curious plants that we know as liver-worts. Like frogs they can live only in wet places; on tide-water faces of cliffs, on rocky river banks, around ponds and springs and even floating on patches of quiet water in marshes.

He-pat-i-cae is the book name of liver-worts. That is confusing, because there is a little pink flower that blooms in the woods and meadows in the spring, that is called the hepatica. We won't say he-pat-i-cae again, and we wouldn't say it even this once, if you didn't need to turn back to that word in Volume II, page 865, of this book, to see some pictures, and to read more about liverworts. There, a scientist who has made a study of life in plants and animals, says: "The liver-worts were probably derived from the algae and, in turn, have given rise to mosses and ferns."

Very likely this is the way the algae managed to turn into liver-worts. You remember the algae learned to cling to rocks, to spread into feathery fronds and to grow bud cells or spores. These are hints of roots and leaves and seeds. If you lift a frond of sea