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the proper stimuli are applied to it, start in its growth into a new plant. Let us see what these stimuli are.
Effect of Water on Dry Seeds. Weigh ten dry navy beans; leave them in water over night; reweigh. How much have they increased in weight? We have already found that water gets into the seed through the micropyle. It can be proved that it gets in through the seed coat as well. If you cover five seeds entirely with paraffin, and in five others cover the hilum, micropyle, and half of the remainder of the coat, a difference in weight and size will be apparent the next morning.
Expansive Force of Germinating Seeds. - The expansive force of germinating seeds is considerable. You have noticed that the bean is considerably larger after soaking.
Fill a small bottle almost full of dry seeds (beans or peas), then fill the space left with water; wire in the cork tightly. Leave the bottle overnight and note the results next morning. Would this force be of use in getting a start under the soil? Have you noticed that the soil is lifted in the garden by the rows of germinating peas and beans just before they come up? Is this due entirely to the expansive force of seeds? Watch future experiments before you attempt a definite an
Will a Dry Seed germinate?Place a layer of moist blotting paper or sawdust in bottom of each of three cups or three tin cans. Soak fifteen navy beans overnight. Place five in each dish. Water one dish so as to cover the seeds; water the second so as to keep sawdust rather moist; let the third remain unwatered. Cover the cups with loose-fitting covers. Make daily observations of the number germinating, and the condition of each for at least ten days. Put the results in tabular form. What amount of water is most favorable for germination of the navy bean?1
The expansive force of germinating seeds. The flower pot to the left was filled with dry beans, a block of wood wired on, and the whole apparatus placed in a pail of water over night. The right-hand figure shows the result.
Water a Factor in Germination. A dry seed will not germinate. Water is absolutely necessary to start the forces at work toward growth. But it is sometimes difficult to determine the amount of water that is most favorable to germination. Some seeds require a great deal of water, others require very little.
Will a Seed grow without Air?- We have already seen that in the germinating corn plant the starch stored in the endosperm was changed to grape sugar by the action of a digestive ferment called diastase. This sugar was then used by the plant as food. 1 See Hunter and Valentine, Manual, page 222.
In other words, the food furnished new material for the plant, and energy for it to push its way through the sawdust or soil. We have proved that energy is invariably released as a result of oxidation. It will be of interest, then, to see
if the grain of corn or other seeds can grow without a supply of oxygen.
A simple method is as follows, although this is not an accurate experiment: Place 25 to 50 soaked beans or peas in each of two wide-mouth bottles, 6 oz. to 12 oz. Cork and seal one; leave the other uncorked, taking care to keep the seeds as moist as in the covered jar. Notice any differences in the seeds for at least one week. Make drawings showing your results.1
A more accurate method of determining this is to exclude air entirely from a glass jar or bottle in which germinating seeds had previously been placed. Air may be exhausted by means of an air pump. If the tube is now sealed by heating under the flame of a burner, the seeds will be left in an air-tight jar. A jar with seeds in same condition, except for lack of air, should be kept as a control experiment.
Why did not the seeds in the covered jar germinate? We have seen that to release the energy contained in a piece of coal we must burn or oxidize it. To do this we must have a constant supply of fresh air containing oxygen. The seed, in order to release the energy contained in its food supply, must have oxygen, so that the oxidation of the food may take place. Hence a constant supply of fresh air is an important factor in germination. It is important that air should penetrate between the grains of soil around a seed. The frequent stirring of the soil enables the air to reach the seed. Air also breaks down some materials in the soil and puts them in a form that the germinating seed can What is at least one reason why the farmer plows and harrows a field? What is at least one important use of the earthworm?
1 See Hunter and Valentine, Manual, page 224.
Oxidation in the Human Body. Exhale strongly through a straw or a glass tube into limewater. The limewater turns milky, showing that oxidation of organic matter has taken place within the body.
If now a glass cylinder in which has been placed some moist blotting paper on which a handful of soaked peas or beans are resting is left overnight in a moderately warm room, and if the air within the jar is tested the following morning, carbon dioxide will be found present. How shall we explain its presence, in view of the above test with the human breath?
Experiment. Place sawdust in each of two small boxes (cigar boxes will do) and plant an equal number of bean, pea, and squash seeds in each. Place one box in a warm room (in the winter near a radiator or stove), the other in a room where the temperature will not exceed 70° Fahrenheit. Be careful to give each box the same conditions of light and moisture. In which box do seeds first germinate? Which box shows the better growth after three weeks have elapsed?
Moderate Temperature Best. - Another factor influencing the germination of seeds is that of temperature. What is the most favorable temperature for the germination of the bean, pea, and squash ?1 From this experiment we find that although a high temperature may stimulate the seed to immediate activity, nevertheless, later, the seeds in moderate temperature do better than those in the heat. The temperature at which different seeds germinate varies greatly. Those of you who have a garden at home know that even some varieties of seeds germinate at lower temperatures than others of the same species; for example, early peas, lettuce, or radish seed. As a general rule, increase in temperature is favorable up to a certain point, beyond which it is injurious to the young plant. Can you determine this danger point from your experiments?
Light has a certain marked effect on young seedlings, which will be considered when we take up the growth of the stem in more detail.
SELECTIVE PLANTING. Although it has been noticed for a long time that healthy seed usually produced healthy plants, it is only within recent years that farmers have begun to appreciate what can be done by selective planting. By selective planting we mean choosing the best plants and planting the seed from these plants with a view of increasing the yield. In doing this we must not necessarily select the most perfect fruits or grains, but must select seeds from the best plants. A wheat piant should be selected not from its yield alone, but from its ability to stand disease and unfavorable conditions. In 1862 a Mr. Fultz, of Pennsylvania, found three heads of beardless or bald
1 See Hunter and Valentine, Manual, page 223.
wheat while passing through a large field of bearded wheat. He picked them out, sowed them by themselves, and produced a quantity of wheat now known as the Fultz wheat (known favorably all over the world). By careful seed selection, some western farmers have increased their wheat production by 25 per cent. This, if kept up all over the United States, would mean over $100,000,000 a year in the pockets of the farm
Boys and girls who have gardens of their own can easily try experiments in selection with almost any garden vegetables. Corn is one of the best plants to experiment with. Gather for planting only the fullest ears and those with the largest kernels. You must also select from the plants those that produce the most ears. Plant such corn grains, carefully selected, in a plot by themselves in the garden, and compare their yield with that of the non-selected corn. The accompanying picture shows what can be done by selection. We find that, by what is known as a law of heredity, like produces like; hence the growth in the case of the selected grains. Not only does the corn produce ears with a greater number of grains, but it may improve upon the quality of the yield.
Improvement of corn by selection; a, original type; b, improved type developed from it.
FOR THE PUPIL
Andrews, Botany All the Year Round, pages 103-119.
American Book Company.
Cornell Nature Study Leaflets. XXVIII, XLII, XLIV. N.Y. Dept. of Agriculture.
FOR THE TEACHER
Goodale, Physiological Botany. American Book Company.
De Candolle, Origin of Cultivated Plants. D. Appleton and Company.
Year Book, U.S. Dept. of Agriculture, 1894, 1895, 1896, 1897, 1898, 1899, 1901.
VII. ROOTS AND THEIR WORK
THE development of a bean seedling has shown us that the root invariably grows first. One of the most important functions of the root to a young plant is that of a holdfast, an anchor to fasten it in the place where it is to develop. __This chapter will show us very many other uses of the root to the plant, the taking in of water, the storage of food, climbing, etc. All other functions than the first one stated arise after the young plant has begun to develop.
Young bean plant, showing primary and secondary roots.
Root System. If you dig up a young bean seedling and carefully wash off 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. În a young plant, notice the general direction taken by the roots. Can you give any reason for the spreading out of the roots in all directions?
Make a drawing of the root system of a seedling; label all its parts.
Downward Growth of Root.
Most of the roots examined take a more or less downward direction. We have already seen that factors outside of the seed call it into activity and cause what we call germination. Might external factors cause the root to grow downward, and if so, what are the factors?
The following apparatus and experiments will throw some light on this question.
The Pocket Garden.2 A very convenient form of pocket germinator may be made in a few minutes in the following manner: Obtain two cleaned four by five negatives (window glass will do); place one flat on the table and place on the glass half a dozen pieces of colored blotting paper cut to a size a little less than the glass. Now cut four thin strips of wood so as to fit on the glass just outside of the paper. Next moisten the blotter,
1 See Hunter and Valentine, Manual, page 20.
2 Ibid., page 233.