A Civic Biology, Presented in Problems

by George W. Hunter

Demonstration.—Nutrients present in some roots.

Uses of the Root.—If one of the seedlings of the bean spoken of in the last chapter is allowed to grow in sawdust and is given light, air, and water, sooner or later it will die. Soil is part of its natural environment, and the roots which come in contact with the soil are very important. It is the purpose of this chapter to find out just how the young plant is fitted to get what it needs from this part of its environment; namely, the soil.

The development of a bean seedling has shown us that the root grows first. One of the most important functions of the root to a young seed plant is that of a holdfast, an anchor to fasten it in the place where it is to develop. It has many other uses, as the taking in of water with the mineral and organic matter dissolved therein, the storage of food, climbing, etc. All functions other than the first one stated arise after the young plant has begun to develop.

A root system, showing primary and secondary roots.

Root System.—If you dig up a young bean seedling and carefully wash the dirt from the roots, you will see that a long root is developed as a continuation of the hypocotyl. This root is called the primary root. Other smaller roots which grow from the primary root are called secondary, or tertiary, depending on their relation to the first root developed.

Downward Growth of Root. Influence of Gravity.—Most of the roots examined take a more or less downward direction. We are all familiar with the fact that the force we call gravity influences life upon this earth to a great degree. Does gravity act on the growing root? This question may be answered by a simple experiment.

Revolve this figure in the direction of the arrows to see if the roots of the radish respond to gravity.

Plant mustard or radish seeds in a pocket garden, place it on one edge and allow the seeds to germinate until the root has grown to a length of about half an inch. Then turn it at right angles to the first position and allow it to remain for one day undisturbed. The roots now will be found to have turned in response to the change in position, that part of the root near the growing point being the most sensitive to the change. This experiment seems to indicate that the roots are influenced to grow downward by the force of gravity.