  When the sweet-peas in the garden were nearly full grown, Uncle George sowed some sweet-peas in a pot. In a fortnight those sown in the pot were about four inches in height, and those in the garden were in flower. “Let us go into the garden, boys,” he said, “and see if we can learn something from the sweet-pea.” In the garden the sweet-peas were really lovely. They looked, as Frank said, like so many beautiful butterflies on the wing; and they filled the air with delicious perfume. “I think,” said Frank, “that our row of sweet-peas is by far the best thing in the garden.” “That is quite true, Frank,” said his uncle, “but it is not so much the flowers we are going to study at present. The sweet-pea is certainly one of our finest flowering plants. It is also one of the most interesting. Can you tell me why we put stakes up for our sweet-pea plants to cling to?” “Because they have long, slender stems—too slender and weak to grow up by themselves,” said Frank. “Quite right, Frank. If the sweet-pea were a wild plant, where would it grow?” “In the hedges,” said Tom. “Right again,” said Uncle George. “If we grow the sweet-pea in the garden, we must imitate its surroundings in the wild state—we must give it a hedge of some kind to cling to, otherwise it would trail along the ground.” “Then it would get choked among the other plants,” said Frank.
“What do you mean by ‘choked,’ Frank?” “Well, it would die for want of air”—— “And light,” his uncle added. “No green plant can live without air and sunlight; and, in order to get these, our weak-stemmed sweet-pea has to climb. It clings to its stronger brethren just as the wild peas do in the hedgerow. Now notice how it climbs. The end part of each leaf consists of little gripping organs called tendrils. These twine tightly round the smallest twigs near them.
“Here is a rose leaf. It is composed of several leaflets, and at its base there are two small, brownish-green things called stipules. If we compare this leaf with the leaf of the sweet-pea, we find that in some points they are similar, but in others very different.
“The rose leaf is called a compound leaf, because it is made up of many small leaflets. The sweet-pea leaf is also a compound leaf, but it has only two leaflets, and these are of enormous size. The rose leaf has two small stipules. The stipules of the sweet-pea leaf are large and green. “If I place the rose leaf beside a sweet-pea leaf, you will notice that the latter has no upper leaflets.” “It has tendrils ‘instead,’” said Frank. “Exactly!” said Uncle George. “These tendrils Young Edible Pea. “We have already learned that plants take in food from the air by means of the green substance in their leaves. The more of this green substance a plant possesses, the more food it can take in from the air. If it sacrifices leaves in order to climb up to the light and air, its amount of the green material must be lessened. But the sweet-pea makes up for this loss of leaves. Can you see how it does so?” “The stipules are very large,” said Frank. “And the lower part of the leaf-stalk is very flat, broad, and green,” added Tom. “Very good,” said Uncle George, “but look at the long, slender stem. It has flat, green, ribbon-like outgrowths on each side throughout its whole length. So, you see, what the plant loses in leaves, it makes up in another way. “Let us now look at the ordinary pea plant. Its leaf has four pairs of leaflets and three pairs of tendrils
“Let us now look at the tendrils of the sweet-pea, and see how they grip their supports. Notice that they begin to twist long before they reach the supporting twig. Then, when they have reached it, they twist round it in the opposite way—just like a piece of string, if you twist it at one end, it untwists at the other.” “Can you see any reason for this coiling before it “You see,” Uncle George continued, “if it were not for that first coiling of the tendril—that is to say, if the tendril grew out straight and only began to twist when it reached the twig—the first breeze of wind would snap the plant from its supports and it would fall to the ground. “Look now, at the young sweet-peas which we grew in the pot. They are without tendrils of any kind. This shows us, I think, that the sweet-pea was at one time a small plant, like its relative the clover. It grew in open places and did not have to struggle for light and air. But, by and by, when strong growing plants took up the soil, it became forced to produce climbing organs or become choked out. And, having turned its leaves into climbing or gripping organs, it made up for the loss of leaves by producing large stipules and green out-growths to stem and leaf.” Exercises on Lesson V.
|
|
