With the fertilized ovules transforming into seeds the ovary undergoes simultaneous appropriate changes and modifications in its structure to give am pie protection to the developing seeds. This secondarily developed and modified ovary enclosing the seeds is called the fruit.
The covering of the mature fruit representing the ovary wall is called the pericarp. The pericarp is usually divisible into three regions, viz., the epicarp, which forms the outermost layer or the epidermis; the mesocarp, which constitutes the major middle portion of the pericarp, and the endocarp, which forms the innermost layer of the pericarp.
The epicarp is usually a one cell thick layer, but in. some cases may include one or more hypodermal layers as in Colocynth. The mesocarp forms the bulk of the fruit and maybe succulent or pithy, or it may consist of several layers of different types of cells or may be composed of spongy parenchyma. However, in all cases, the vascular strands ramify in the tissue of the mesocarp. The endocarp may consist of only one layer of cells or of several modified layers forming a thick woody structure. This woody structure, which is often called the ‘stone’, forms a hard casing of the seeds.
The external characters of fruit are manifested on its outermost covering the epicarp, which normally consists of a single layer of epidermal cells. The epicarp frequently possesses stomata, usually in small numbers. Well-formed solitary crystals (prisms) of calcium oxalate occur in certain cells of the epicarp of Coriander and Vanilla. Characteristic cells with thickened walls occur in the epicarp of Vanilla. The epicarp of some fruits remains covered with striated cuticles as in Aniseed and Caraway. Trichomes and hairs also frequently occur on the epicarp of many fruits, particularly the young ones.
Classification of The Fruits
In addition to the ovary, other floral members such as the thalamus or sepals or bracts and axis of the inflorescence may take part in the formation of the fruit. On the basis of this diversified development, fruits are broadly classified into three groups, viz., simple fruits, aggregate fruits, and compound fruits.
When the single ovary of a flower develops into a fruit with or without accessory parts, it is called a simple fruit. A simple fruit may be dry or fleshy. The dry simple fruits may be dehiscent or indehiscent when mature.
The dry dehiscent fruits of pharmacognostic importance include the following types:
- Legume or pod: This type of simple fruit develops from a superior one-chambered ovary and dehisces by both sutures, e.g., Senna pod, Tamarind.
- Follicle: This is a similar fruit to a legume, but dehisces by one suture only, e.g., Calotropis.
- Capsule: This is a many-seeded fruit which develops from a superior ovary and dehisces in a number of ways, e.g., Stramonium, Opium poppy, Cotton.
Most of the simple dry indehiscent fruits of pharmacognostic importance belong to the following types:
- Caryopsis: It is a one-seeded fruit developing from a superior ovary and has a very thin pericarp, which is fused with the seed-coat, e.g., Rice, Wheat, and Maize.
- Cremocarp: This is a two-seeded fruit developing from an inferior ovary. When ripe the fruit splits apart into two indehiscent one-seeded parts, which remain attached to its axis, e.g., Anise, Coriander, Fennel, Caraway, Dill.
The fleshy simple fruits of pharmacognostic value mostly belong to the following types:
- Drupe and Drupaceous fruits: These are one or more seeded fruits developing from superior ovaries, with prominent fleshy or fibrous mesocarps and hard or stony endocarps, e.g., mango, Prune, Palm, and Coconut.
- Berries: These are many seeded, fleshy or pulpy fruits developing from both superior and inferior ovaries, e.g., Capsicum, Orange, Tomato, Colocynth, Guava, Paw-paw, Banana.
A collection of many simple fruits on one main axis is called an aggregate fruit. The component simple fruits of an aggregate fruit develop from the free carpels of a single flower. Such aggregates of simple fruits borne by a single flower are also called an ‘etaerio’. Aggregate fruits of pharmacognostical significance include the etaerio of achenes such as Hips, Clematis Rose and etaerio of achenes such as Hips, Clematis, Rose, and etaerio of follicles such as Star anise, Vinca and Aconite.
Compound or multiple or composite fruits are formed when the whole inflorescence with its large number of flowers becomes fleshy and develops into a compact single fruit, as in Fig. Hops, Pineapple and Jackfruit.
There are a large number of fruits, which constitute pharmaceutically and commercially useful drugs. Some of them are described below in the form of Monographs as representative examples for the students so that they can also describe other fruit drugs.