“Did you notice how they pushed their way through the stones and pieces of rock, and even moved them as they grew!”
“I did!” answered each of the girls.
“I thought it wonderful,” continued Mary Frances, “but I supposed it was a fairy way of growing.”
“No,” Jack shook his head; “that is the way all plants grow, whether small or large, only they grow slowly. Notice the smallest roots. They are hollow and have very thin delicate coverings.”
“You will see why in a minute,” he went on, “but now I wish to call your attention to something else. In between the stones and sand you will notice decaying leaves and——”
“Humus!” cried Mary Frances jumping up in excitement.
“Good!” he said. “Humus soup is what the plants eat. The tiny roots draw it up through their thin walls. In the humus soup is not only decaying vegetable matter, but very tiny bits of mineral matter, too—like pepper and salt for the plant, maybe.”
The girls laughed.
“Listen!” he went on earnestly; “for any plant to produce one pound of dry matter, the roots must take up from 300 to 500 pounds of water.”