Part 5

Frank and Tom were quite puzzled. They could not understand why the roots should come at the bottom in two of the twigs and not in the other two.

“First of all, then,” said Uncle George, “these new roots were made from materials which came from inside the plant. These building materials are carried through the plant dissolved in water—just as you dissolve sugar in your tea. Water containing these dissolved stuffs in a plant is called sap.

“We have seen, by our first three experiments, that water travels up the wood part of the stem. This experiment shows us that sap travels down the stem in the layers outside the wood. For, when I removed the outer layers and left a bare ring of wood, the flow of the sap was stopped and the new roots formed there.”

“And where does this sap come from first of all?” Tom asked.

“It is really formed in the leaf first of all. I think I told you that plants take most of their food from the air by means of their green leaves. In the great quantities of water which pass up the wood and into the air from the leaves there is always a very little mineral matter dissolved. This small quantity of mineral matter comes from the soil. This, along with water and the large quantity of matter taken from the air, are changed, inside the leaf, into a fluid which we call sap.

“Our four experiments show us that water travels up through the wood-layer from soil to leaf; and also that sap travels down through one of the outside layers of the stem.”

Questions on Lesson III.

1. How does water travel in a plant? How can you prove this? 2. If we enclose a leafy plant in a glass vessel, we see that water is given off by the leaves. How is it that we do not see this water when the plant is grown in the open air? 3. What is “sap”? Where is it first formed? How does it travel in the twig or stem? 4. If we keep ferns growing under a glass bell—or in a glass case—we never have to water them. Can you explain this?

IV.—SNOWDROP, CROCUS, AND TULIP.

The boys watched the growth of the crocuses in water and in soil from day to day, and made sketches of them once a week. Fed by the food contained in the corm, the top buds of the crocus grew longer. Then the scales moved apart and the yellow flower was seen. Round about it were four or five narrow green leaves, each having a pretty white stripe down the middle. Both leaves and flower were encircled at the base by long white sheaths.

The crocus grown in the pot did not seem to thrive much better than the one in the water. Both flowers remained closed for a long time after they were full grown.

At last, on one fine sunny day, they opened out wide at the top, and the boys could see right down into them. In the evening they closed up again. Next day was a dull day, and the crocus flowers remained closed.

The snowdrops were also watched and sketched. Their growth was somewhat different. From the centre of the little bulb two green leaves first appeared. These leaves were much broader and thicker than those of the crocus. From between these leaves a little white, flat object grew up. This the boys at once recognised as the spathe or bag containing the flower. Then more green leaves came up. The flower-stalk grew longer. The spathe split open, and the flower-bud appeared.

This bud grew until it became a beautiful white bell hanging downwards.

In a large pot Uncle George had planted a few tulip bulbs. They were not completely covered with soil, so that their growth could be watched. Their growth was similar to that of the snowdrop. The leaves came first. They were rolled firmly round each other. As each large, broad, green leaf unrolled, another rolled-up leaf was seen under it. These leaves were rolled round a thick stalk, to which they were attached. When the last leaf unrolled, a single flower was seen at the top of the stalk. This flower remained closed up like the crocus. When at length, however, the warm sun shone in the window, the tulip flowers opened out very wide indeed; in fact, they became almost saucer-shaped.

Then Uncle George dug the snowdrop and crocus out of their pots. He washed the roots and asked the boys to compare them with those grown in water.

“The plants grown in soil seem stronger in flower and leaves,” said Frank. “But the greatest difference is in the corm and bulb.”

“That is right, Frank,” said Uncle George. “Look at the crocus corms. They have both shrunk a great deal, because they have been used up to form what has grown out of them. But the one grown in soil has formed a new corm, which will produce new flowers next year. This new corm has grown upon the top of the old one. The crocus grown in water has also produced a new corm, but it is too small to produce a flower next year.

“Then, again, take the snowdrop. The one grown in the soil has produced two or three new bulbs, while that grown in water has not. These new bulbs were the side buds we noticed between the scales when we opened out our snowdrop bulb. In both snowdrops the old bulb has been completely used up to form green leaves and flower.

“But the bulb grown in soil has not only produced flowers and green leaves. It has gathered up enough material from soil and air to form new bulbs for next year.”

1. Snowdrop Flower—A, the spathe. 2. Crocus Plant. 3. Old and Young Corms of Crocus. 4. Young Snowdrop Flower enclosed in its spathe. 5. Crocus Flower. 6. Tulip Flower dissected.

Uncle George then divided the crocus flower with his knife from top to bottom.

“At the very bottom of the flower,” he said, “you see the ovary, or seed-vessel, containing the tiny seeds. From the seed-vessel a long thin rod or tube stretches to the very mouth of the flower. You can also see the remains of the spathe which once enclosed the whole flower.”

“And what are those three things covered with orange-coloured dust?” asked Tom.

“These,” said his uncle, “are the stamens or pollen-boxes; and the orange-coloured powder is the pollen. This pollen is carried about from flower to flower by the bees. Pollen is necessary for the production of seeds.

“Do you know why the seed-vessel of the crocus is so far down under the ground?

“It is because the crocus flowers in winter-time, and the frost might kill the young seeds. Underground they are safe from frost. The snowdrop is a hardy flower, and, besides, the walls of its seed-vessel are very thick.

“The tulip, if grown outside, flowers much later than the other two plants.