There is a plant called the “amphibious knotweed.” This is a rather difficult name, I know. This word “amphibious” is applied to something that can live both in water and on land; and this plant grows sometimes in the pond or river, and sometimes on the shore.
When on land, its stem is covered with the hairs which serve to keep meddlesome insects from climbing up to its pretty balls of pink flowers. In the water there is no danger of any such attack from insects; and so when it happens to grow in the pond or river, this knowing little plant does not trouble itself to clothe with hairs its stem, but leaves this quite smooth.
Next summer I hope you will hunt up the amphibious knotweed, and will compare the smooth water stem with the hairy one that grows on land.
STEMS AND SEED LEAVES
The smaller plants usually have green stems. The larger ones have brown, woody stems, such as you see in bushes and trees; for the trunk of the biggest tree in the world is nothing but a great stem.
The delicate green stems die down to the ground during the cold winter. Sometimes the whole plant dies, the root below as well as the stem above ground. But often the root (or what we usually call the root) lives, and sends up a fresh stem the next year.
But the woody stems live through the winter, and put out fresh leaves and branches the next spring.
Without a magnifying glass, it is difficult to see of just what the green stems of the small plants are made up; and these you can pass by for the present. But if your teacher will cut across the stem of a large rose, you can see here an outer covering, the green skin; within this, a ring of woody material; and in the center of the stem, a soft white stuff called “pith.”
When we were reading about seed leaves, I told you that by the stem and leaves of a plant you could tell whether it brought into the world more than one seed leaf.