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matters are taken in far in excess of the immediate needs of the plant. Such minerals are stored in the stem and leaves.

Need of Mineral Matter for Growth. Plants will not grow well without certain of these mineral substances. This can be proved by the growth of seedlings in a so-called nutrient solution. Such a solution contains all the mineral matter that a plant uses for food.1 Mineral Matter necessary for Growth of Young Plants. Obtain three jars; put distilled water in one, nutrient solution (without ferric chloride) in another, and nutrient solution plus ferric chloride in the third. Place germinating corn or bean seedlings in the jars so that roots extend down into the liquids. Observe the growth of the three lots of seedlings. Decide which of the three jars is most favorable to growth.

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Nitrogen in a Usable Form necessary for Growth of Plants. - We learned that humus is made up of decayed plant and animal bodies. A chemical element needed by the plant to make protoplasm is nitrogen. This element cannot be taken from either soil water or air in a pure state, as is the case with the other chemical elements used by the plant in the manufacture of protoplasm. Nitrogen is usually obtained from the organic matter in the soil, where it exists with other substances in the form of nitrates. Nitrogen is found in such form in all decaying material; hence the use of fertilizers.2

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Bacteroids forming

from filamentous structures in the cells of a root.

Relation of Bacteria to Nitrogen. It has been known for a long time that clover, peas, beans, and other legumes, cause the ground to become more favorable for growth of other plants. The reason for this has been discovered in late years. On the roots of the

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Ferric chloride (FeClg)

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0.50 gram 0.005 gram

(Do not put the ferric chloride into the solution in the first place, but add a drop of it to each bottle when the seedlings are put in.)

2 Other important plant foods found in soil, but which are frequently used up by plants growing therein, are potash and phosphoric acid. Both of these substances are made soluble so as to be taken in by the root by the action of the carbon dioxide in the soil.

plants mentioned are found little swellings or tubercles; in the tubercles exist millions of tiny plants called bacteria, which take out nitrogen from the atmosphere and fix it so that it can be used by the plant; that is, they form nitrates for the plants to use. These bacteria, alone of all the living plants, have the power to take the free nitrogen from the air and make it over into a form that can be used by the roots.

Nitrogen

Nitrates

Nitrogen

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Nitrates t

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This fact is made use of by careful farmers who wish to make as much as possible from a given area of ground in a given time. Such plants as are hosts for the nitrogen-fixing bacteria are planted early in the season. Later these plants are plowed in and a second crop is planted. The latter grows quickly and luxuriantly because of the nitrates left in the soil by the bacteria which lived with the first crop. For this reason, clover is often grown on land in which it is proposed to plant corn, the nitrogen left in the soil thus giving nourishment to the young corn plants. The annual yield of the average farm may be greatly increased by this means.

Tubercles on clover roots.

Forms of Roots and their Relation to the Life of the Plant. Roots assume various forms. The form or position of the root is usually dependent on the needs of the plant, the roots acting to help it succeed in certain localities.

Food Storage. The use to the plant of the food stored in the taproot may be understood if we think of the life history of the parsnip. Such a plant produces no seed until near the end of the second year of its existence. After forming seeds it dies. The

food stored in its root enables it to get an early start in the spring, so as to be better able to produce seeds when the time comes.

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Examples of other roots storing food are carrot, radish, yam, sweet potato, etc.

Corn roots, showing prop roots developed at first node above ground.

Demonstration. - Test a cross section of the parsnip root with iodine. In which part of the root is starch stored? Test another cross section with nitric acid and ammonia. Which part of the root contains stored food?

WATER ROOTS. - In the duckweed, a plant living in water, the roots are short and contain few root hairs. The water supply is so great that few root hairs have been called forth. The water hyacinth is another example of slight development of roots. The plant is buoyed up by the water and does not need strong roots to hold it firm.

ADVENTITIOUS ROOTS. - Roots are

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Some plants, as strawberry, couch grass, and many others, develop new plants by striking root at any point on the reclining stem where it touches the ground. This fact is made of use by practical gardeners in the layering of plants.

Examine the Indian corn for another kind of adventitious root. Here they serve as props for the tall stem. In the young seedlings of corn, notice how early these roots develop. Also notice the manner in which they arise on the stem.

AIR ROOTS. In tropical forests, where the air is always warm and moist, some plants have come to live above the soil on the trunks of trees, or in other places where they can get a favorable foothold. Such plants are called epiphytes or air plants. The tropical orchid seen in our greenhouses is an example. Examine the roots of such a plant. Notice how thick they are. They are usually provided with a spongy tissue around the outside which has the function of absorbing water.

PARASITIC ROOTS. — A few plants live on other living plants, and develop by the aid of nourishment taken at their expense. Such a plant or animal is called a parasite. The plant or animal on which the parasite lives is called the host. The mistletoe is an example of a parasitic plant. An examination of its roots shows that they have bored their way into the stem of the host. These roots not only penetrate the bark but push toward the center of the tree, taking nourishment from the cells there. The dodder is another seedbearing plant which has this habit. Dodder produces from seed, but is unable to live alone after it has passed the seedling stage, and will die if it cannot find a suitable host. It is found on many common weeds, as jewel weed and golden-rod. Many of the lower plants live as parasites, among them being mildew, rusts, and smuts found on roses, grain, and corn.

REFERENCE BOOKS

FOR THE PUPIL

Andrews, Botany All the Year Round. Chap. II.

American Book Company.

Goff and Mayne, First Principles of Agriculture. American Book Company. Atkinson, First Studies of Plant Life, Chaps. IX, XI, XII. Ginn and Company. Coulter, Plant Studies, Chap. V. D. Appleton and Company.

Stevens, Introduction to Botany, pages 31-44. D. C. Heath and Company.

FOR THE TEACHER

Goodale. Physiological Botany. American Book Company.

Gray, Structural Botany, pages 27-39, 56–64. American Book Company.
Leavitt, Outlines of Botany, pages 27-39, 56–60. American Book Company.
Setmer-Moor, Practical Plant Physiology. The Macmillan Company.
Green, Vegetable Physiology, Chaps. V. VI. J. and A. Churchill.

MacDougal, Plant Physiology. Longmans, Green, and Company.

HUNTER'S BIOL. 7

VIII. BUDS AND STEMS

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Structural Differences between the Stem and the Root. Wash carefully the earth from the roots of a pea seedling that you have grown in the laboratory. Try to make out the following points: (1) note the differences in color between the stem and roots; (2) compare the manner in which the root and stem give off lateral branches. Notice that the leaves and lateral branches from a stem are more or less regular in position, while the small roots have no regular method of leaving the primary root. The places on the stem where leaves are given off are known as nodes, the part of the stem between being called an internode.

In a growing stem of any woody plant, notice the end of the stem; the bud at the termination is a future stem. It is well for us to remember that a stem is a developed bud, as we shall see when we take up the work on the bud more in detail.

One difference which is very noticeable between the stem and the root is the color, the young root being whitish or gray, and

A pocket garden which has been kept in complete darkness for several weeks. Notice the condition of stems and leaves.

the young stem being green. The following experiment will serve to explain this difference:

Effect of Absence of Light on Young Plants. - Plant some peas in sawdust within a box, or wide-mouthed bottle which has been previously blackened so that no light is admitted to the interior. Grow some of the same seed in a box alongside the covered material, giving each the same amount of heat and moisture. After the young plants have grown, take one out, compare note the difference in color.

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it with the ones grown in the light, and
Might the absence of light account for the color of the root?

The seedlings which have been grown in darkness show some other interesting conditions. The stems are long and more or less reclining on the sawdust. The leaves are hardly worthy of the name, being reduced to little scales. We know that they are

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