and usually light is seen. The energy set free by the oxidation of fuel may be transformed at one time into light, at another time into motion, or again into heat.

It is probably true that the liberation of energy in living plants is somehow due to the action of oxygen. The process, however, is doubtless extremely complicated, and just what takes place no one knows. Certainly oxygen in some form is essential for the life of every plant and animal. That this is true of plants, the following experiment will show.

79. To prove that seeds need air in order to grow. Laboratory Study No. 39. Demonstration or Home Work.

Secure two wide-mouthed bottles and place in the bottom of each a wet sponge or some wet blotting paper, and pour enough water in each bottle just to cover the sponge or paper. Fill both bottles with pea seeds that have been soaked in water for twenty-four hours. Insert a tightly fitting cork into the mouth of one of the bottles to exclude the air. Leave the other bottle open to the air, and add enough water from day to day to make up for the loss by evaporation. Put both bottles in a warm place.

1. Describe this experiment, showing in what respects the conditions are the same for both groups of seeds.

2. In what one respect do the two groups of seeds differ? 3. At the end of several days examine both bottles of seeds, and state your observation concerning the amount of growth in each bottle.

4. State clearly your conclusion as to the necessity of air for growth of pea seedlings.

80. Relation of oxygen and carbon dioxid to oxidation. We have now demonstrated that seedlings will not grow without air. Biologists have proved conclusively that oxygen is the element in the air that is essential for the work of all plants, and that without it they die. Hence, we may conclude, as in the case of the furnace, that the necessary energy

of a plant is in some way set free by oxygen acting upon plant compounds. When oxidation of compounds containing carbon takes place, we find that carbon dioxid is produced (11). Now if processes like oxidation are carried on in plants, we should expect to find that CO2 is formed. The following experiment proves clearly that such is the case.

81. To prove that carbon dioxid is formed during the growth of young seedlings. Laboratory Study No. 40.

In the bottom of two large jars (fruit jars will answer) place some wet blotting paper. Fill one of the jars half full of germinating peas, and place a small wide-mouthed bottle full of lime water on top of the seeds. Screw the top of the jar on tightly. In the other jar place a bottle of lime water and cover as in the previous jar. At the end of twenty-four hours or more examine the lime water in both jars.

1. Describe the preparation of the experiment.

2. Compare the condition of the lime water in both jars. What has caused the change in the lime water in both jars?

3. Air, as we proved, contains a little carbon dioxid. Bearing this fact in mind, account for the difference in the appearance of the lime water in the two jars.

4. What gas, therefore, do you find to be given off during the growth of young seedlings?

II. RESPIRATION

82. Respiration in plants. It should be clear from our study thus far that all plants require oxygen, and that this oxygen brings about in plants a process resembling oxidation at least in the releasing of heat and other forms of energy and in the producing of carbon dioxid. These various processes take place in each living plant cell. Hence, every cell uses oxygen and must necessarily form carbon dioxid. This process which goes on in every living cell is respiration.

In green plants during the night, when carbon dioxid is not being used for starch manufacture, this gas is given off to the surrounding air, which probably is not true to any great extent during the daytime. The taking in of oxygen and the giving off of carbon dioxid by plants corresponds to breathing in animals. Breathing is carried on in plants through the thin walls of roots, through the lenticels of stems, and through the stomata of leaves. The principal distinction, therefore, between breathing and respiration includes the taking in of oxygen, the use of oxygen by the cells (in oxidation), and the giving out of carbon dioxid. The process of breathing must not be confused with that of carbohydrate manufacture, and the following outline will show the fundamental difference between the two.

CHAPTER VII

REPRODUCTION IN PLANTS

I. THE STRUCTURE AND FUNCTIONS OF FLOWERS

83. Necessity of plant reproduction. Every one knows that plants like peas, beans, and corn live but one year. Shrubs and trees, while they often live for many years, finally die. This is true of all plants. It is evident, therefore, that unless there were some means of producing new plants to take the place of those now living, all forms of plant life would soon cease to exist. The process by which new plants are formed is known as reproduction. In the higher plants this process is carried on by flowers, the function of which is to produce seeds which will develop into new plants. We are now to study the various parts of flowers and to consider the work of each part in this process of reproduction.

84. Study of tulip flower (spring study). Laboratory Study No. 41.

Material: While the trillium is a more satisfactory flower for beginning the study of the process of reproduction, the danger that the wild flowers will become exterminated seems to make the study of the tulip advisable, especially in large city high schools. The two flowers, however, are usually in season at the same time, and if possible at least a few of the trilliums should be secured for demonstration. If this is impossible, the distinction between calyx and corolla should be taught from the apple blossom or other com mon flower.

A. Floral envelopes. Most flowers have parts shaped more or less like leaves which have either green or

bright colors. These parts are arranged in one or more circles and make up the floral envelopes. 1. How many parts are there in the floral envelopes of a tulip? State the color or colors of these parts in the flower you are studying.

2. When there are two circles to the floral envelopes, an outer composed of green parts and an inner made up of brightly colored parts (as in the trillium or the apple blossom), distinct names are given to the various parts. The outer circle is called the calyx and its parts are known as sepals; the inner circle is called the corolla and each of its parts is called a petal.

a. State the number and color of the sepals in the calyx of the trillium.

b. How many petals do you find in the corolla? Describe their color.

3. Draw a side view of a tulip before it has fully opened. Label flower-stalk and floral envelopes.

B. Essential organs.

- In the central part of the flower are the organs without which the work of the flower cannot be performed. For this reason they are called the essential organs.

1. The organs arranged in a circle just within the floral

envelopes are known as stamens. State the

situation and the number of stamens in the tulip. What is the number of stamens in the trillium or apple blossom?

2. Each stamen consists of a stalk called the filament and an enlarged part known as the anther.

Name and describe each of the parts of a stamen. 3. Make a drawing twice its natural size of one of the stamens. Label filament, anther.

4. Find a flower the stamens of which have a powdery substance known as pollen. Which part of the stamen produces the pollen?

5. The organ at the center of the flower is called the

pistil. It consists of three divisions at the top