The corolla is the innermost series or whorl of modified leaves in the perianth. Individual units of the calyx are sepals, which are typically green, leaflike, and function to protect the young flower. The calyx is the outermost series or whorl of modified leaves. In most flowers the perianth is differentiated into two groups. If the perianth is relatively undifferentiated, or if its components intergrade in form, the individual leaflike parts are termed tepals. The perianth (also termed the perigonium) is the outermost, nonreproductive group of modified leaves of a flower. From the receptacle arise the basic floral parts. In some taxa the receptacle can grow significantly and assume an additional function. The receptacle is typically at the very tip of the floral axis (derived from the original apical meristem). The receptacle or floral receptacle (also termed a torus, although “torus” can also be used for a compound receptacle see Inflorescence Parts, page 484) is the tissue or region of a flower to which the other floral parts are attached. Bracteoles, where present, are typically paired. (If a pedicel is absent, the flower attachment is sessile.) Flowers may be subtended by a bract, a modified, generally reduced leaf a smaller or secondary bract, often borne on the side of a pedicel, is termed a bracteole or bractlet (also called a prophyll or prophyllum). The basic parts of a flower, from the base to the apex, are as follows ( Figure 9.13). With powdered flowers the pollen grains, portions of the fibrous layer of the anther wall and the papillose epidermis of the stigmas are obvious features. Of first importance is the occurrence, size, shape and wall structure of pollen grains. Characteristic fragments of the anther wall are diagnostic of the presence of flowers. A characteristic papillose epidermis may sometimes be present on the stigmas of the gynaecium. Delicate coloured fragments of the corolla can often be distinguished in coarsely powdered drugs. The epidermal cells of the corolla often have a papillose or striated cuticle. The bracts, calyx and, to a lesser extent, corolla have a leaf structure and will yield such elements as epidermis with stomata, glandular and covering hairs, mesophyll cells, oil glands and crystals. The flower stalk or pedicel has a stem structure and in the powdered form exhibits the appropriate elements. Daphne Evans BA MA, in Trease and Evans' Pharmacognosy (Sixteenth Edition), 2009 Anatomy William Charles Evans BPharm BSc PhD DSc FIBiol FLS FRPharmS.
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