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vii A flower, in its most perfect form, consists of an outer envelope composed of several leaf-like divisions called the calyx, an inner series of similar leaves called the corolla, and a number of small bodies situated within these denominated stamens and pistils. The usual arrangement of these parts may be seen in Fig. 5. The outer series of leaves, forming the calyx, are termed sepals; they are usually green. The leaves of the inner series, or corolla, are called petals, and, being generally highly coloured, form the most conspicuous part of the flower; in our figure they are of the same number as the sepals and alternate with them, but in many flowers several series of petals are developed. The calyx is sometimes coloured like the corolla, and can then only be distinguished from the latter by its position, as in Lilies and most other endogenous flowers; the floral leaves are then collectively styled a perianth. Where only one series of floral leaves is present, it is considered as a calyx, whether coloured or not. Sometimes the calyx is deciduous, that is, it falls off before the flower opens, as in the Poppy tribe, and in some plants both calyx and corolla are wanting. The sepals are occasionally united at their base into a tube, and the same is frequently the case with the petals, as in the Foxglove, Primrose, and many other flowers. The calyx is frequently reduced to a mere rim, as in some of the Umbelliferæ; while in the Compositæ, the order to which the Dandelion and Thistle belong, it is represented only by a circle of hairs or scales beneath the corolla, and is then denominated a pappus. In the Grasses there is no regular calyx or corolla, these envelopes being represented by two series of scale-like bracts, the outer of which are called glumes, the inner paleæ. Sometimes, as in the Calla and the wild Arum of our hedges, the floral organs are enclosed in one large bract, which receives the name of a spathe.

The petals are usually equal in number to the sepals, or some multiple of that number, and such flowers are called by botanists symmetrical; when the contrary is the case the flower is said to