Part 4

“The food store in bulbs and corms is the same as that in seeds,” said Tom.

“The food supply of the bulb is contained in the thick, fleshy scale-leaves, while in the corm it is in the stem,” said Frank.

“Very good,” said Uncle George. “It also shows us, I think, that we ourselves owe a great deal to the plant world.”

Exercises on Lesson II.

1. Split an onion (or tulip bulb) down the centre, and compare it with the snowdrop bulb. Draw it, giving special attention to the middle part. 2. Take a potato and a crocus corm. Observe them both carefully, and find out (1) how they resemble each other, and (2) how they differ. 3. Explain how it is that a hyacinth grows so well in water. 4. Take any underground stem (e.g., iris or Solomon’s seal) and compare it with a crocus corm. Notice the marks of underground scale-leaves on the former.

III.—WHAT GOES ON INSIDE A PLANT.

“We have seen how an ordinary twig is built up,” said Uncle George. “Let us now try to find out what goes on inside the twig; and in order to do this we shall have to perform one or two simple experiments.”

Uncle George took two wide-mouthed glass jars. They were both perfectly dry, and each could be closed with a large, tight-fitting cork. He placed some fresh green leaves inside one of the jars. The other remained empty. Then both jars were tightly corked up, and both corks covered outside with wax.

“That is experiment number one,” he said, as he placed both jars in the window.

He next took a small plant which was growing in a pot. He wrapped the pot up in thick, dry paper, so that the paper covered up everything but the plant. The edges of the paper were tied tightly round the lower part of the stem of the plant with a string. The plant was put in the window, and over it Uncle George placed a glass bell-jar.

“The third experiment is much simpler,” he said. “You see I just put one of the willow twigs into a glass half filled with water, and into the water I pour some red ink. Frank, place a white pansy in the coloured water beside the willow twig.”

Uncle George’s fourth experiment was as follows:—

He placed four willow twigs in a glass of water. But from two of these twigs he first removed a broad ring of the bark and outer layers, leaving about an inch of the wood bare near the lower end of the twig.

“Now,” said he, “we will come back in about an hour, and I think we shall find that some change has taken place in each of our first three jars.

“The fourth glass one will have to be left for several weeks; and we must take care to keep water always in the glass containing these four twigs.”

About an hour afterwards, Uncle George and the boys came to look at the experiments.

“Let us examine experiment one first,” said Uncle George.

“The empty jar is just the same as when we put it there,” said Tom. “The jar containing the leaves is all dimmed, and there are tiny drops of water on the inside of it.”

“Where did that water come from, Tom?”

“It must have come out of the leaves.”

“Exactly so! Now look at the second experiment, and you will see that the bell-jar which covered both plant and pot is also dimmed with moisture. Pot and soil were securely covered up, so that this moisture on the glass must have come from the leaves of the plant. Where do you think this water really comes from?”

“From the soil in the pot,” said Frank. “If we did not water those plants which we keep in pots, they would die.”

“Then we have learnt that water travels up the stems of plants,” said Uncle George, “also that it is drawn from the soil and is given off by the leaves. The third experiment, where we placed a twig in coloured water, will, I think, show us which part of the stem the water travels up.”

Uncle George peeled the bark off the lower end of the willow twig which was placed in the mixture of red ink and water. He removed all the layers until he came to the wood. The wood was stained red. He cut slice after slice off the twig, and it was found that the coloured water had gone quite an inch up through the wood. None of the other layers of the twig were stained red.

“It travels up through the wood-layer,” said Frank. “And look at the pansy flower. It was white when we put it into the glass, now it is all streaked with red.”

“The flower itself,” said Uncle George, “is not near the coloured water.”

“The water must have travelled up the long stalk to the flower,” said Frank.

The fourth experiment was left in the window, and two or three weeks passed before any change was noticed in any of the four twigs which had been placed in the water. Then roots began to grow. In the two whole twigs these roots grew out at the bottom end. But in those twigs from which the belt of outer layers had been removed, it was quite different. Here the roots grew out—not at the bottom, but just where the ring of bare wood began and at the top of it.