A Civic Biology, Presented in Problems. George W. Hunter
filled with a number of nearly ovoid bodies, attached along one edge of the inner wall. These we recognize as the young seeds.
The pod of a bean, pea, or locust illustrates well the growth from the flower. The pod, which is in reality a ripened ovary with other parts of the pistil attached to it, is considered as a fruit. By definition, a fruit is a ripened ovary and its contents together with any parts of the flower that may be attached to it. The chief use of the fruit to the flower is to hold and to protect the seeds; it may ultimately distribute them where they can reproduce young plants.
The Necessity of Fruit and Seed Dispersal to a Plant.—We have seen that the chief reason for flowers, from the plant's standpoint, is to produce fruits which contain seeds. Reproduction and the ultimate scattering of fruits and seeds are absolutely necessary in order that colonies of plants may reach new localities. It is evident that plants best fitted to scatter their seeds, or place fruits containing the seeds some little distance from the parent plants, are the ones which will spread most rapidly. A plant, if it is to advance into new territory, must get its seeds there first. Plants which are best fitted to do this are the most widely distributed on the earth.
The development of an apple. Notice that in this fruit additional parts besides the ovary (o) become part of the fruit. Certain outer parts of the flower, the sepals (s) and receptacle, become the fleshy part of the fruit, while the ovary becomes the core. Stages numbered 1 to 7 are in the order of development.
How Seeds and Fruits are Scattered.—Seed dispersal is accomplished in many different ways. Some plants produce enormous numbers of seeds which may or may not have special devices to aid in their scattering. Most weeds are thus started "in pastures new." Some prolific plants, like the milkweed, have seeds with a little tuft of hairlike down which allows them to be carried by the wind. Others, as the omnipresent dandelion, have their fruits provided with a similar structure, the pappus. Some plants, as the burdock and clotbur, have fruits provided with tiny hooks which stick to the hair of animals, thus proving a means of transportation. Most fleshy fruits contain indigestible seeds, so that when the fruits are eaten by animals the seeds are passed off from the body unharmed and may, if favorably placed, grow. Nuts of various kinds are often carried off by animals, buried, and forgotten, to grow later. Such are a few of the ways in which seeds are scattered. All other things being equal, the plants best equipped to scatter seeds or fruits are those which will drive out other plants in a given locality. Because of their adaptations they are likely to be very numerous, and when unfavorable conditions come, for that reason, if for no other, are likely to survive. Such plants are best exemplified in the weeds of the grassplots and gardens.
[2] To the Teacher.—Any simple plant or animal tissue can be used to demonstrate the cell. Epidermal cells may be stripped from the body of the frog or obtained by scraping the inside of one's mouth. The thin skin from an onion stained with tincture of iodine shows well, as do thin sections of a young stem, as the bean or pea. One of the best places to study a tissue and the cells of which it is composed is in the leaf of a green water plant, Elodea. In this plant the cells are large, and not only their outline, but the movement of the living matter within the cells, may easily be seen, and the parts described in the next paragraph can be demonstrated.
Reference Books
elementary
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Andrews, A Practical Course in Botany, pages 250–270. American Book Company.
Atkinson, First Studies of Plant Life, Chaps. XXV-XXVI. Ginn and Company.
Bailey, Lessons with Plants, Part III, pages 131–250. The Macmillan Company.
Coulter, Plant Life and Plant Uses. American Book Company.
Dana, Plants and their Children, pages 187–255. American Book Company.
Lubbock, Flowers, Fruit, and Leaves, Part I. The Macmillan Company.
Newell, A Reader in Botany, Part II, pages 1–96. Ginn and Company.
advanced
Bailey, Plant Breeding. The Macmillan Company.
Campbell, Lectures on the Evolution of Plants. The Macmillan Company.
Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book Company.
Darwin, Different Forms of Flowers on Plants of the Same Species. Appleton.
Darwin, Fertilization in the Vegetable Kingdom, Chaps. I and II. Appleton.
Darwin, Orchids Fertilized by Insects. D. Appleton and Company.
Müller, The Fertilization of Flowers. The Macmillan Company.
V. PLANT GROWTH AND NUTRITION. CAUSES OF GROWTH
Problem.—What causes a young plant to grow?
(a) The relation of the young plant to its food supply.
(b) The outside conditions necessary for germination.
(c) What the young plant does with its food supply.
(d) How a plant or animal is able to use its food supply.
(e) How a plant or animal prepares food to use in various parts of the body.
Laboratory Suggestions
Laboratory exercise.—Examination of bean in pod. Examination and identification of parts of bean seed.
Laboratory demonstration.—Tests for the nutrients: starch, fats or oils, protein.
Laboratory demonstration.—Proof that such foods exist in bean.
Home work.—Test of various common foods for nutrients. Tabulate results.
Extra home work by selected pupils.—Factors necessary for germination of bean. Demonstration of experiments to class.
Demonstration.—Oxidation of candle in closed jar. Test with lime water for products of oxidation.
Demonstration.—Proof that materials are oxidized within the human body.
Demonstration.—Oxidation takes place in growing seeds. Test for oxidation products. Oxygen necessary for germination.
Laboratory exercise.—Examination of corn on cob, the corn grain, longitudinal sections of corn grain stained with iodine to show that embryo is distinct from food supply.
Demonstration.—Test for grape sugar.
Demonstration.—Grape sugar present in growing corn grain.
Demonstration.—The action of diastase on starch. Conditions necessary for action of diastase.
What makes a Seed Grow.—The general problem of the pages that follow will be to explain how the baby plant, or embryo, formed in the seed as the result of the fertilization of the egg cell, is able to grow into an adult plant. Two sets of factors are necessary for its growth: first, the presence of food to give the young plant a start; second, certain stimulating factors outside the young plant, such as water and heat.
Three views of a kidney bean, the lower one having one cotyledon removed to show the hypocotyl and plumule.
If