In some plants tendrils are _leaflets_ (Chap. XI). Examples are the sweet pea and the common garden pea. In Fig. 171, observe the leaf with its two great stipules, petiole, six normal leaflets, and two or three pairs of leaflet tendrils and a terminal leaflet tendril. The cobaea, a common garden climber, has a similar arrangement. In some cases tendrils are _stipules_, as probably in the green briers (smilax). The _petiole_ or _midrib may act as a tendril_, as in various kinds of clematis. In Fig. 172, the common wild clematis or “old man vine,” this mode is seen. =Twiners.=—The entire plant or shoot may wind about a support. Such a plant is a =twiner=. Examples are bean, hop, morning-glory, moon-flower, false bittersweet or waxwork (_Celastrus_), some honeysuckles, wistaria, Dutchman’s pipe, dodder. The free tip of the twining branch _sweeps about in curves_, much as the tendril does, until it finds support or becomes old and rigid. 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. [Illustration: 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