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vous system of man and other large animals, as the ox, elephant, and whale.
VARYING SIZES OF LIVING THINGS. Plant cells and animal cells may live alone or they may form collections of cells as tissues. Some plants are so simple in structure as to be formed of only one kind of tissue cells. Usually living organisms are composed of several groups of such tissues. Examples have been given. It is only necessary to call attention to the fact that such collections of tissues may form organisms so tiny as to be barely visible to the eye; as, for instance, some water-loving flowerless plants or many of the tiny animals living in fresh water or salt water, such as the hydra, small worms, and tiny crustaceans. On the other hand, among animals the bulk of the elephant and whale, and among plants the big trees of California, stand out as notable examples.
Relation to Organic and Inorganic Matter. The inorganic matter covering the earth, as air and water, and forming the great mass of its bulk, is made use of by plants and animals. The latter make their homes in earth, air, or water; they breathe the oxygen of the atmosphere; they use the water for drinking; but in the main their food consists of organic matter. Plants, on the other hand, use the elements contained in the soil, air, and water, not only for food, but also to make the living matter of their own bodies. In some mysterious way, of which we shall later learn something, plants take up inorganic and organic substances from the soil and air and transform them into organic matter. This organic matter in turn becomes food for animals.
In the last chapter we found that the classes of substances in an animal or plant and the organic food substances have a similar composition. Let us now consider chemically the substance which forms the basis of all living things.
Protoplasm. Living matter, when analyzed by chemists in the laboratory, seems to have a very complex chemical composition. It is somewhat like a proteid in that it always contains the element nitrogen. It also contains the elements carbon, hydrogen, oxygen, and a little sulphur, and perhaps phosphorus. Calcium, iron, silica, sodium, potassium, and other mineral matters are usually found in very minute quantities in its composition. We believe that the matter out of which plants and animals are formed, although a very complex building material and almost
impossible of correct analysis, is nevertheless composed of certain chemical elements which are always present. To this living matter the name protoplasm has been given.
Protoplasm, then, is made up of certain chemical elements, combined in definite proportions. What is of far more importance to us is the fact that it is distinguished by certain properties which it possesses and which inorganic matter does not possess.
Properties of Protoplasm. - Plants and animals are largely made up of living matter. Let us study its properties:
(1) It It responds to influences or stimulation from without its own substance. Both plants and animals are sensitive to touch or stimulation by light, heat, or electricity. Leaves turn toward the source of light. Some animals are attracted to light and others repelled by it; the earthworm is an example of the latter. Many other instances might be given. Protoplasm is thus said to be irritable.
(2) Protoplasm has the power to move and to contract. Muscular movement is a familiar instance of this power. Plants move their leaves and other organs. One-celled animals change their form.
(3) Protoplasm has the power of taking up food materials, of selecting the materials which can be used by it, and of rejecting the substances that it cannot use. A commercial sponge, the dried skeleton of an animal, if placed in water, will swell up with the water absorbed by it, but the water thus taken in is not used by the dead skeleton. Protoplasm, however, in the tiny parts of the root of a plant called the root hairs, takes in only the material which will be of use in forming food or new protoplasm for the plant. An animal selects only such food as it wants, and refuses to eat material that it does not use as food.
(4) Protoplasm grows, not as inorganic objects grow, from the outside,1 but by a process of taking in food material and then changing it into living material. To do this it is evident that the same chemical elements must enter into the composition of the food substances as are found in living matter. The simplest plants
1 Experiment. - Make a strong solution of alum (two spoonfuls of powdered alum to half a glass of water). Suspend in the glass a thread with a pebble attached to the lower end. Notice where and how crystals of alum grow.
and animals have this wonderful power as well developed as the most complex forms of life.
(5) Protoplasm, be it in the body of a plant or an animal, uses oxygen. It breathes. Thus the food substances taken into the body are oxidized, and either release energy for growth, movement, etc., or form new protoplasm.
(6) Protoplasm has the power to rid itself of waste materials, especially those which might be harmful to it. A tree sheds its leaves partly to get rid of the accumulation of mineral matter in the leaves. Plants and animals alike pass off the carbon dioxide which results from the very processes of living, the oxidation of foods or parts of their own bodies. Animals eliminate wastes containing nitrogen through the skin and the kidneys.
(7) Protoplasm can reproduce, that is, form other matter like itself. New plants are constantly appearing to take the places of those that die. The supply of living things upon the earth is not decreasing; reproduction is constantly taking place. In a general way it is possible to say that plants and animals reproduce in a very similar manner. We shall study this more in detail later.
To sum up, then, we find that living protoplasm has the properties of sensibility, motion, growth, and reproduction alike in its simplest state as a one-celled plant or animal and when it enters into the composition of a highly complex organism such as a tree, a dog, or a man.
BOOKS FOR REFERENCE
FOR THE PUPIL
Leavitt. Outlines of Botany. American Book Company.
Atkinson. First Studies of Plant Life. Chap. XI. Ginn and Company.
FOR THE TEACHER
Goodale. Physiological Botany. American Book Company.
Huxley and Martin. Course of Elementary Instruction in Practical Biology. The
Sedgwick and Wilson. General Biology. Henry Holt and Company.
Wilson. The Cell in Development and Inheritance. The Macmillan Company.
Structure of a Simple Flower. For the following exercise, the buttercup and Sedum (stonecrop) are good. They may be obtained in the fall.1
The expanded portion of the flower stalk, which holds the parts of the flower, is called the receptacle. The green leaflike parts covering the unopened flower are called the sepals. Sometimes the sepals are all joined or united in one piece. Taken together, they are called the calyx. Notice that the sepals come out in a circle or whorl on the flower stalk. How many sepals do you find? In what respect do they resemble leaves? Are there any evidences as to their use or function?
The more brightly colored structures are the petals. Taken together, they form the corolla. The corolla is of importance, as we shall see later, to make the flower conspicuous.
Compare the petals and sepals in this flower. Are sepals and petals in any respects like leaves?
A flower, however, could live without sepals or petals and still do the work for which it exists. The essential organs of the flower are within the so-called floral envelope. They consist of the stamens and carpels (or pistils). The latter are in the 'center of the flower. The structures with the knobbed ends are called stamens. How many stamens do you find, and what is their position?
A flower of Sedum from above; A, anther; C, carpel; F, filament; P, petal; S, sepal.
A flower of Sedum, from the side;
In a single stamen the boxlike part at the end is the anther; the stalk is called the filament. The anther is in reality a hollow box in which a dustlike material called pollen is produced. It is necessary for the life of the plant that the pollen get out of the anther. Try to find how it gets out.
Pistil. Each carpel or pistil is composed of a rather stout base called the ovary, and a more or less lengthened portion rising from the ovary called the style. The upper end of the style, which in some cases is somewhat broadened, is called the stigma. The stig
matic surface usually secretes a sweet fluid in which grains of pollen from flowers of the same kind can grow.
Draw one of the flowers in your notebook. Show the flower stalk or peduncle and all the above-mentioned parts carefully labeled. Keep any notes that you may have made on the work on the flower.1
Pollen. Pollen grains of various flowers, when seen under the microscope, differ greatly in form and appearance. Some are relatively large, some small, some rough, others smooth, some spherical, and others angular. They all agree, however, in having a thick wall, with a thin membrane under it, the whole inclosing a mass of protoplasm. At an early stage the pollen grain contains but a single cell. When we see it, however, we can distinguish two nuclei in the protoplasm. Hence we know that at least two cells exist there.
Experiment. Germination of the Pollen Grain. Make a solution of fifteen grams of granulated sugar in one hundred cubic centimeters of water. Place on each of several glass microscopic slides a few drops of the solution and sprinkle with pollen taken from well-opened flowers of sweet pea or a nasturtium. Place on the slides some very thin and small bits of cover glass, and with these prop up the cover slip which is placed over the sugar solution. Leave them for a few hours under a bell jar with a piece of moist sponge to keep the air in the jar moist. Examine the slides from time to time under the microscope. The grains of pollen will be found to germinate, a long threadlike mass of protoplasm growing from it into the sugar solution. The presence of this sugar solution was sufficient to induce growth.
Three stages in the germination of the pollen grain in sugar solution. Drawn under the compound microscope.
Demonstration under Microscope. -Pollen tubes growing in dilute sirup. When the pollen grain germinates, one of the nuclei enters the threadlike growth (this growth is called the pollen tube; see figure). The pollen tube is therefore a long threadlike cell, which is artificially stimulated to growth by the sugar solution, but which in nature is brought into existence by the presence of the sweet liquid which exudes from the surface of the stigma. The cell which grows into the pollen tube is known as the sperm cell.
Structure of the Pistil.-Let us now examine the structure of the pistil more in detail. (Use for this purpose any large lily.) Cut the pistil length
1 Laboratory directions for other work on flowers may be found in Hunter and Valentine, Manual, pages 51-63.