Each kind of plant usually coils in only one direction. Most plants coil against the sun, or from the observer’s left across his front to his right as he faces the plant. Examples are bean, morning-glory. The hop twines from the observer’s right to his left, or with the sun.
Fig. 172.—Clematis climbing by Leaf-tendril.
Suggestions.—136. Set the pupil to watch the behaviour of any plant that has tendrils at different stages of maturity. A vigorous cucumber plant is one of the best. Just beyond the point of a young straight tendril set a stake to compare the position of it. Note whether the tendril changes position from hour to hour or day to day. 137. Is the tip of the tendril perfectly straight? Why? Set a small stake at the end of a strong straight tendril, so that the tendril will just reach it. Watch and make drawing. 138. If a tendril does not find a support what does it do? 139. To test the movement of a free tendril draw an ink line lengthwise of it, and note whether the line remains always on the concave side or the convex side. 140. Name the tendril-bearing plants that you know. 141. Make similar observations and experiments on the tips of twining stems. 142. What twining plants do you know, and which way do they twine? 143. How does any plant that you know shoot up? 144. Does the stem of a climbing plant contain more or less substance (weight) than an erect self-supporting stem of the same height? Explain.
CHAPTER XVIII
THE FLOWER—ITS PARTS AND FORMS
The function of the flower is to produce seed. It is probable that all its varied forms and colours contribute to this supreme end. These forms and colours please the human fancy and add to the joy of living, but the flower exists for the good of the plant, not for the good of man. The parts of the flower are of two general kinds—those that are directly concerned in the production of seeds, and those that act as covering and protecting organs. The former parts are known as the essential organs; the latter as the floral envelopes.
Fig. 173.—Flower of a Buttercup in Section.
Envelopes.—The floral envelopes usually bear a close resemblance to leaves. These envelopes are very commonly of two series or kinds—the outer and the inner. The outer series, known as the calyx, is usually smaller and green. It usually comprises the outer cover of the flower-bud. The calyx is the lowest whorl in Fig. [173].
The inner series, known as the corolla, is usually coloured and more special or irregular in shape than the calyx. It is the showy part of the flower, as a rule. The corolla is the second or large whorl in Fig. [173].