Thus any twining plant with a heart-shaped leaf, white and green above and purple beneath, is called by them guaco (R.
Metamorphosis.It has already been pointed out that each kind of member of the body may present a variety of forms. For example, a stem may be a tree-trunk, or a twining stem, or a tendril, or a thorn, or a creeping rhizome, or a tuber; a leaf may be a green foliage-leaf, or a scale protecting a bud, or a tendril, or a pitcher, or a floral leaf, either sepal, petal, stamen or carpel (sporophyll); a root may be a fibrous root, or a swollen tap-root like that of the beet or the turnip. All these various forms are organs discharging some special function, and are examples of what Wolff called modification, and Goethe metamorphosis.
The most characteristic members of the order are twining plants with generally smooth heart-shaped leaves and large showy white or purple flowers, as, for instance, the greater bindweed of English hedges, Calystegia sepium, and many species of the genus Ipomaea, the largest of the order, including the "convolvulus major" of gardens, and morning glory.
The dodder is a genus (Cuscuta) of leafless parasites with slender thread-like twining stems. The flowers stand singly in the leaf-axils or form few or many flowered cymose inflorescences; the flowers are sometimes crowded into small heads.
The jalap plant has slender herbaceous twining stems, with alternately placed heart-shaped pointed leaves and salver-shaped deep purplish-pink flowers.
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