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 common 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 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 common 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 which together are known as the stigma, and the remainder of the pistil known as the ovary. Describe the pistil of the tulip (and of the trillium) as to position, shape, and color of its parts. 6. Make a drawing twice its natural size of the pistil. Label stigma, ovary. 7. Cut thin cross sections of a well-developed ovary, 9. (Optional.) Make a drawing (corresponding in size to that 85. Study of the gladiolus flower (autumn study). Laboratory Study No. 42. Note to the teacher. Be careful to remove each flower close to the central stalk, so that the ovary may not be injured. A. Parts of the flower. 1. Remove the two leaves at the base of the flower, since these leaf-like organs do not belong to the flower. The outer brightly colored parts of the flower are called the floral envelopes. These colored parts unite to form a greenish tube below. a. Count and record the number of divisions of which the floral envelopes are composed. b. State whether or not these divisions are all of the 2. The slender stalks with purple tips, inside the floral |