Flowers and their friends

by Margaret Warner Morley

TUBE CELLS.

The top of a tree is a long way from the roots. Yet the leaves must have food from the roots, and the roots must have food from the leaves.

It is not an easy matter to move all this food material up and down, you may be sure.

I wonder how you would manage it?

Why, you say, if I had to raise sap from under the ground to the top of the tree, I should certainly build some pipes and have a pump at the top.

That is the way the plant has decided. So pipes there are, plenty of them,—pipes or tubes of many sizes and shapes.

You know how cells grow, lying next each other. Well, tube cells are long and contain protoplasm in the beginning. They lie end to end. But, you see, it would not be very easy for the sap to pass through millions of cell walls on its way up.

So when the protoplasm has built a row of cells with good thick walls, it passes out through thin places or openings it has left in the walls. The end partitions between the tube cells are thin and break away, and lo and behold! we have a long, strong tube with nothing in it but air. Up this tube the sap creeps or down it the sap runs. A great many of these tubes, which are as fine as hairs or much finer in some cases, are needed in a plant. They run all through the stems and out into the leaves. They are collected into bundles, and form part of the veins and the framework of leaves. I do not know what the plant would do without them.