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The frond grows from a flat disc-shaped gemma, the two sides of which are alike. Either side may fall uppermost; and then of the developing shoot, the side exposed to the light "is under all circumstances the upper side which forms stomata, the dark side becomes the under side which produces root-hairs and leafy processes."
In these the gradual formation of the root-cap could be watched throughout, with merely a small lens. I do not know a better way to impress the nature of the root on the pupil's mind. These forming roots might also be marked very early, and so be shown to carry onward their root-cap on the growing-point. Root-hairs.
Bean and Sunflower are the best for the purpose. Begin by telling the pupils to prepare for their first lesson a description of the roots of their seedlings. Those grown on sponge or paper will show the development of the root-hairs, while those grown on sand are better for studying the form of the root.
These are an example of secondary roots, which are roots springing laterally from any part of the stem. The Sweet Potato has both fleshy and fibrous roots and forms secondary roots of both kinds every year. Some of the seedlings will probably show the root-hairs to the naked eye. These will be noticed hereafter. Tap-root. 2. Multiple root of Pumpkin. 3. Napiform root of Turnip. 4.
In those grown in sand, they become so firmly united to the particles of soil, that they cannot be separated, without tearing the hairs away from the plant. This will suggest the reason why plants suffer so much from careless transplanting. The root-hairs have the power of dissolving mineral matters in the soil by the action of an acid which they give out.
As a root grows older the root-hairs die, and it becomes of no further use for absorption. But it is needed now for another purpose, as the support of the growing plant. In trees, the old roots grow from year to year like stems, and become large and strong.
II. Same, showing how fine particles of sand cling to the root-hairs. Cover a piece of polished marble with moist sawdust, and plant some seeds upon it. When the seedlings are somewhat grown, remove the sawdust, and the rootlets will be found to have left their autographs behind. Wherever the roots, with their root-hairs have crept, they have eaten into the marble and left it corroded.
They have said that the caulicle was the part to grow first, and have spoken of the arched form of the young stem. Their attention should also be drawn to the root-hairs, which are well seen in Corn, Wheat, and Oats. They absorb the liquid food of the plants. A secondary office is to hold the seed firmly, so that the caulicle can enter the ground.
This is shown in Red Clover, which may be sown on the surface of the ground. It puts out root-hairs, which attach themselves to the particles of sand and hold the seed. These hairs are treated more fully in the lessons on roots. By Charles Darwin. London. Leaves of Seedlings.
They then absorb these solutions for the nourishment of the plant. The acid given out was first thought to be carbonic acid, but now it is supposed by some experimenters to be acetic acid, by others to vary according to the plant and the time. The action can be shown by the following experiment, suggested by Sachs. I. Seedling of Sinapis alba showing root-hairs.