tailieunhanh - THE SOIL AND THE PLANT

You have perhaps observed the regularity of arrangement in the twigs and branches of trees. Now pull up the roots of a plant, as, for example, sheep sorrel, Jimson weed, or some other plant. Note the branching of the roots. In these there is no such regularity as is seen in the twig. Trace the rootlets to their finest tips. How small, slender, and delicate they are! Still we do not see the finest of them, for in taking the plant from the ground we tore the most delicate away. In order to see the real construction of a. | THE SOIL AND THE PLANT You have perhaps observed the regularity of arrangement in the twigs and branches of trees. Now pull up the roots of a plant as for example sheep sorrel Jimson weed or some other plant. Note the branching of the roots. In these there is no such regularity as is seen in the twig. Trace the rootlets to their finest tips. How small slender and delicate they are Still we do not see the finest of them for in taking the plant from the ground we tore the most delicate away. In order to see the real construction of a root we must grow one so that we may examine it uninjured. To do this sprout some oats in a germinator or in any box in which one glass side has been arranged and allow the oats to grow till they are two or more inches high. Now examine the roots and you will see very fine hairs similar to those shown in the accompanying figure forming a fuzz over the surface of the roots near the tips. This fuzz is made of small hairs standing so close together that there are often as many as 38 200 on a single square inch. Pg 26 Fig. 17 shows how a root looks when it has been cut crosswise into what is known as a cross section. The figure is much increased in size. You can see how the root-hairs extend from the root in every direction. Fig. 18 shows a single root-hair very greatly enlarged with particles of sand sticking to it. These hairs are the feeding-organs of the roots and they are formed only near the tips of the finest roots. You see that the large coarse roots that you are familiar with have nothing to do with absorbing plant food from the soil. They serve merely to conduct the sap and nourishment from the root-hairs to the tree. When you apply manure or other fertilizer to a tree remember that it is far better to supply the fertilizer to the roots that are at some distance from the trunk for such roots are the real feeders. The plant food in the manure soaks into the soil and immediately reaches the root-hairs. You can understand this better