At the base of many leaves are a pair of scales called stipules; the petiole or leaf-stalk is generally cylindrical, but frequently triangular, and in grasses it is flat and surrounds the stem, this is called a sheath; when leaves are narrow and not expanded into a lamina, as in the pine tribe, they are said to be "acicular."
The stalks which bear the flowers are called "pedicels," at the base of which are a pair of scales called "bracts;" when these are large and expanded, so as to enclose the flowers, they are called "spathes" (this is seen in the arum), and when there are a number of flower-stalks arising from one point the bracts there collected are called an "involucre." A flower consists of several parts, the outermost green scales, composing a set, are called the calyx, and each part of it, is called a "sepal," within this is the "corolla" or that coloured part which forms the most characteristic feature of the flower, each part of the corolla is called a "petal;" when the corolla consists of but one piece, it is called "monopetalous," and when of many, "polypetalous."
The forms of corolla vary according to the form and the mode in which the petals are placed, whether united or separated, and to what extent, whether regular or irregular; the most usual forms are the following:—
Campanulate
(Bell-shaped), Canterbury Bell.
Rotate (Wheel-shaped),
Woody Nightshade.
Hypocrateriform
(Salver-shaped), Phlox.
