FRUIT AND SEEDS

FRUIT

A true fruit is formed as a result of cell division expansion and differentiation in the ovary wall (placenta). The ovary is transformed into fruit as a result of stimuli received from pollination and developing seeds. The wall of ovary develops into pericarp of  the fruit that is differentiated into epicarp, mesocarp, and endocarp. During pollination the pollen grains release auxin that induces the fruit development.

STRUCTURE OF FRUIT

A true fruit consists of two main parts the seed and the pericarp (fruit flesh). The pericarp consists of three layers- upper epicarp, middle mesocarp and inner endocarp.

TYPES OF FRUITS

Fruits are of three main types

1-SIMPLE FRUITS;  

the fruits that develop from a single monocarpellary or multicarpellary syncarpous ovary are called simple fruits. These are further of two types:

A-dry simple fruits; these fruits have dry pericarp not differentiated into three layers. these are further of three types.

(i)-Dehiscent dry fruits;

Legume; a fruit developed from a monocapellary superior ovary which dehisces from both the sutures into two halves -pea

Follicle;- which dehisces from one suture only –calotropis

Siliqua; develop from a bicapellary superior ovary with a replum or false septum. Dehisces along two sutures -brassica

Capsule; dehiscent dry fruit which dehisces along more than two suture in different planes.

(ii)-Schizocarpic dry fruits

Lomentum; a legume like fruit that dehisces transversely into one seeded indehiscent compartments -tamarindus

Cremocarp; develops from an inferior ovary, splits longitudinally into two indehiscent halves called mericarps -cariandrum sativum.

Regma; it breaks into as many segments as there are carpels -ricinus.

Carcerule; here it breaks into four indehiscent parts with one seed per locule-ocimum.

(iii)Indehiscent dry fruits

Achene; a small indehiscent one seeded fruit with a hard and leathery pericarp that remains free from seed coat -mirabilis jalapa.

Caryopsis; small indehiscent one seeded fruit with a hard and leathery pericarp fused with seed coat - wheat, rice

Cypsela; a one seeded fruit that develops from a multicarpellary ovary with persistent calyx - tridex

Nut; large indehiscent one seeded fruit with a hard and stony fruit wall - chesnut.

Samara; a dry indehiscent one seeded fruit in which pericarp is modified into wings- chilbil.

B-Fleshy simple fruits; fruits with fleshy pericarp distinguished into epicarp mesocarp and endocarp;

Berry; a fleshy many seeded fruit with massive juicy and pulpy pericarp-tomato grapes.

Hesperidium; a fleshy many seeded fruit with a firm hard and leathery pericarp- citrus, lemon, orange

Pepo;  a large fleshy fruit with pulpy pericarp -melon, cucumber

Drupe;-  a fleshy one seeded fruit with the inner hard stony pericarp enclosing a seed-mango, wall nut, peach, cherry.

Balausta; a fleshy fruit with many chambers and many seeds -pomegranate

Amphisarca; a fleshy fruit with woody pericarp and edible placenta- wood apple

Pome; a false fruit that develops from thalamus with true fruits inside containing seeds-apple pear etc

2-AGGREGATE FRUITS

Fruit developed from multicarpellary apocarpous ovary; comprised of many fruitlets;

Etaerio of follicles; fruit consisting of many follicles arranged on thalamus-calotropis

Etaero of achenes;  an aggregate of achenes -strawberry

Etaerio of drupes; an aggregate of drupes- rasberry

Etaerio of berries; an aggregate of berries -anona squamosal

MULTIPLE OR COMPOSITE FRUITS;

the fruits that develop from the complete inflorescence;

Sorosis; fruit developed from a spike or spadix inflorescence - pine apple, mulberry

Syconus; fruit developed from Hypanthodium inflorescence - ficus.  

                                                     SEED

The seed is a developed ovule. Development of the fertilized ovule into the mature seed involves several different parts. From the outside to inwards these are as follows:

• The zygote develops into an embryo.
• The integuments of the ovule become the seed coat of the mature seed. This sometimes consists of two distinct coverings, a typically firm outer coat, the testa, and a generally thin, membranous inner coat, the tegmen.
• The nucellus may persist in some genera as a thin layer - the perisperm
• The endosperm accumulates reserves of food and its fullest development is rich in carbohydrates, fats, proteins and growth
• The funiculus forms the stalk of the seed. Hilum marks the point of attachment to the stalk
• Micropyle remains as a pore on the surface of seed

Structure of Dicot and Monocot Seeds

Structure of Dicot non-endospermic seed (bean seed):

The seeds of bean like those of other legumes are formed within the pod, which is a ripened ovary. The seed is attached to the inside of the pod by the funiculus or seed stalk. When the seeds are shed, the funiculus breaks off, leaving a prominent scar, the hilum. Just below the hilum can be seen the

micropyle and above the hilum is the ridge formed by the raphe. The bean seed has two seed coats outer testa and inner tegmen. Each seed encloses an embryo. The bulk of embryo consists of large cotyledons which stores Most of the food of seed. On the side of the seed, opposite the raphe at the micropylar end the cotyledons form cotyledonary node. Attached to it is found the radical.  Plumule has differentiated two well-defined leaves which fold over the growing tip. These become the first true leaves of the bean plant on germination. The portion between radical and cotyledonary node is called hypocotyl. The portion between plumule and hypocotyl is called epicotyls. In this seed and in all seeds of this type, there is no endosperm, this tissue is already consumed by the developing embryo.

Structure of Monocot, endospermic grain (maize grain ):

It is one seeded fruit called caryopsis or grain because pericarp (fruit wall) is fused with testa. Seed coat is the outer brownish layer of the grain. In this, seed and fruit walls are fused together. Endosperm comprises the major part of grain and is filled with reserve food. It is composed of two regions Outer single layered aleurone layer mainly made up of aleurone proteins. Inner starchy endosperm. It is separated from embryo by a layer called epithelium. Embryo contains a single lateral cotyledon called scutellum and embryo axis with plumule and radicle at its two ends. Root cap protects the tip of radicle. Radicle is surrounded by a protective sheath called coleorhiza. Plumule is also protected by a covered sheath known as coleoptile.