Flowers and their friends

by Margaret Warner Morley

But what makes the sap run up the tubes?

Now you are asking questions! It took a long time for people to find that out, for there is more than one reason why the sap runs up.

For one thing, the root cells keep drawing in water and other things, and the fluid already in is pushed up by that behind; so there is a sort of pump at the bottom of the plant, you see,—a force pump. The sun shining on the leaves and stems evaporates the water above, and the water below then easily takes its place; so there is a sort of suction pump at the top.

Then the tubes are so very fine that the fluid in them tends to move up, just as water will soak up into a towel if the fringe happens to get into the water; for you know that if you hang a towel so that the fringe dips into a basin of water, after awhile the whole towel will be wet, as a result of what we call capillary attraction. For all these reasons the sap creeps up the stems through the tubes the cells have made.

Every plant has these tubes, from the tiniest weed in the garden to the tallest forest tree. Although so small, they are often very prettily marked by lines and dots.

STRENGTHENING CELLS.

Plants need something more than cells of working protoplasm and something more than tubes, just as we need more than flesh and blood vessels.

We would be in a sad plight if we had no bones to keep us in place, and plants would be in a sad plight if they had no—well, not exactly bones, but something to serve the same purpose.

Think of the weight a tree has to bear. You could not begin to lift the crown of a large tree, yet the tree trunk has to hold it up in the air. Not only that,—it has to hold on to it when the wind blows, which is a much harder task. Even small bushes and tender garden plants have quite a weight to bear and quite a task to keep their leaves and stems from being blown away. They could never hold on to them if it were not for the wood and other tough cells they have,—never in the world.