3. Make a diagram greatly enlarged of a piece of root prepared as directed above. Label cortex, central cylinder, fibers of central cylinder. B. Root-hairs. Note to the Teacher.- Root-hairs may be grown for study as follows: Cover the bottom of as many Petri dishes as are needed with a layer of blue blotting paper. Soak the paper with water and lay several grains of soaked barley, oats, or corn upon the bottom of each dish. Put the covered dishes in a warm place for several days. When the root-hairs have developed, wipe the moisture from the inside of the covers, quickly replacing the latter. If Petri dishes are not available, two clean glasses of any convenient size may be used instead. Cover one of the plates with layers of wet blotting paper, put the soaked grains in position, and cover with the second glass, fastening the two together with threads or strings. Stand one end of the preparation thus made in a jar with enough water to reach the lower edge of the blotting paper. Examine first with the naked eye and then with a hand magnifier the roots of sprouted grains, developed as described above. Notice tiny outgrowths from the sides of the roots; these outgrowths are called root-hairs. 1. Look at the very tip of the root and state whether root hairs are there present or absent. 2. State whether the root-hairs are longest near the tip or in the direction of the grain. 3. Make a drawing much enlarged to show the shape of one of the roots including the root-tip and the various lengths of root-hairs. Label root-tip, roothairs. C. Microscopical structure of the tip of a root. (Optional.) Examine with the aid of the low power of the compound microscope a root-tip mounted on a slide in drop of water and covered with a cover glass. Make a sketch very much enlarged to show 1. The outline of the root including the tip. 2. A loose mass of cells covering the lower end of the root which make up the root-cap. 3. Label root-tip, cells of the root-cap. 56. The functions of roots. - Laboratory Study No. 30. A. Roots as organs for holding the plant to the soil. Secure a vigorously growing plant in a pot (e.g. a rubber plant) or better try the following experiment on a good sized weed in a field. Attach to the stem just above ground level a spring balance. Pull on the balance until the plant shows signs of letting go its hold on the soil, then note the reading in pounds on the scale. 1. In your own words describe what was done. 2. How much force in pounds was exerted on the plant? 3. What important function of roots is shown by this experiment? B. Roots as organs for absorbing soil-water. (Before proceeding further with the root study, the osmosis experiments, 44-53, should be performed if they have not already been done.) Study the diagram of a root-hair in the text-book (Fig. 12) and if possible examine with the low power of the microscope some of the younger (shorter) roothairs. Each root-hair is an elongated part of an outer cell of the root. 1. Draw in your note-book a diagram of a root-hair, labeling cell-wall, thin layer of protoplasm, cellsap, and nucleus. 2. What separates the soil-water from the cell-contents? 3. Recall the characteristics of cellular structure as given in 42. Now state which is the more dense, the soil-water or the cell-contents. 4. In which direction, therefore, will there be the greater movement of liquid in the process of osmosis? 5. State several characteristics that adapt root-hairs for absorbing soil-water. C. Roots as organs for transmitting soil-water. Place some seedlings or weeds in red ink so that only the 1. Describe the experiment as it was performed. 3. Make a sketch about an inch in diameter of the cross D. Roots as organs for the storage of food. Cut some slices about an inch thick from parsnips or other fleshy roots, and divide each slice vertically in halves. Put the pieces in water and boil for a few moments to partially cook them. Pour iodine solution over some of the pieces; to others add strong nitric acid; boil still other pieces in a test tube with Fehling's solution. 1. Describe the preparation of each of the experiments, and state in each case your observations. 2. What do you conclude as to the presence or absence of each of three of the food substances in various parts of the fleshy root you are studying? 3. What function of roots do these experiments demonstrate? 57. Adaptations of roots for holding to the soil. One of the most obvious functions of roots is that of holding plants firmly in the ground. If the soil is carefully removed from the roots of a weed or a tree, these roots will be found to extend outward in all directions to a distance even greater than do the branches above ground. When one remembers the tremendous force exerted upon trees by high winds, the necessity for this extensive root anchorage will be evident. In our dissection of the root even of a young plant we found FIG. 10.-Roots of a tree, showing method of transplanting a large tree. (Courtesy of Isaac Hicks and Sons, Westbury, Long Island.) that the central cylinder was composed of tough fibers which are made up of elongated wood-cells (similar to those shown in Fig. 15). As a plant grows older, these central cylinders become so thick and tough that they will resist an enormous strain without breaking. 58. Adaptations of roots for absorbing and transmitting soil-water. A second function of roots we found to be that of absorbing soil-water and transmitting it to the stem. The whole outer surface of young roots is covered with a single layer of thin-walled cells which form the epidermis. Many of these cells develop tubular outgrowths known as root-hairs (see 56, B). By studying Fig. 12 it will be evident that each root-hair consists of a cell-wall lined by a thin layer of protoplasm. The interior of the cell is largely filled with cell-sap. On the outside of each root-hair is soilwater. All the conditions necessary for osmosis are therefore present. The cell-wall is the membrane FIG. 13.- Portion of a root-hair with ad- |