Science Fair Project Encyclopedia
In botany, a fruit is the ripened ovary, together with its seeds, of a flowering plant. In cuisine, when discussing fruit as food, the term usually refers to just those plant fruits that are sweet and fleshy, examples of which would be plum, apple, and orange. However, a great many common vegetables, as well as nuts and grains, are the fruit of the plants they come from. Fruits that might not be considered such in a culinary context include gourds (e.g. squash and pumpkin), maize, tomatoes, and green peppers. These are fruits to a botanist, but are generally treated as vegetables in cooking. Some spices, such as allspice and nutmeg, are fruits. Rarely, culinary "fruits" are not fruits in the botanical sense, such as rhubarb in which only the astringent stalk, or petiole, is edible. Indeed, under European Union trade rules a carrot is defined as a fruit, presumably because fruits are taxed at a higher duty and carrot jam is a popular Portuguese dish.
The term false fruit is sometimes applied to a fruit, like the fig (a multiple-accessory fruit; see below) or to a plant structure that resembles a fruit but is not derived from a flower or flowers. Some gymnosperms, such as yew, have fleshy arils that resemble fruits and some junipers have berry-like, fleshy cones.
With most fruits pollination is a vital part of fruit culture, and the lack of knowledge of pollinators and pollenizers can contribute to poor crops or poor quality crops. In a few species, the fruit may develop in the absence of pollination/fertilization, a process known as parthenocarpy. Such fruits are seedless. A plant that does not produce fruit is known as acarpous, meaning essentially "without a developing ovule-bearing structure".
After an ovule is fertilized in a process known as pollination, the ovary begins to expand. The petals of the flower fall off and the ovule develops into a seed. The ovary eventually comes to form, along with other parts of the flower in many cases, a structure surrounding the seed or seeds that is the fruit. Fruit development continues until the seeds have matured. With some multiseeded fruits the extent of development of the flesh of the fruit is proportional to the number of fertilized ovules.
The wall of the fruit, developed from the ovary wall of the flower, is called the pericarp. The pericarp is often differentiated into two or three distinct layers called the exocarp (outer layer - also called epicarp), mesocarp (middle layer), and endocarp (inner layer). In some fruits, especially simple fruits derived from an inferior ovary, other parts of the flower (such as the floral tube, including the petals, sepals, and stamens), fuse with the ovary and ripen with it. When such other floral parts are a significant part of the fruit, it is called an accessory fruit. Since other parts of the flower may contribute to the structure of the fruit, it is important to study flower structure to understand how a particular fruit forms.
Fruits are so varied in form and development, that it is difficult to devise a classification scheme that includes all known fruits. It will also be seen that many common terms for seeds and fruit are incorrectly applied, a fact that complicates understanding of the terminology. Seeds are ripened ovules; fruits are the ripened ovularies or carpels that contain the seeds. To these two basic definitions can be added the clarification that in botanical terminology, a nut is a type of fruit and not another term for seed.
There are three basic types of fruits:
- Simple fruit
- Aggregate fruit
- Multiple fruit
Simple fruits can be either dry or fleshy and result from the ripening of a simple or compound ovary with but one pistil. Dry fruits may be either dehiscent (opening to discharge seeds), or indehiscent (not opening to discharge seeds). Types of dry, simple fruits (with examples) are:
- achene - (buttercup)
- capsule - (Brazil nut)
- caryopsis - (wheat)
- fibrous drupe - (coconut, walnut)
- follicle - (milkweed)
- legume - (pea, bean, peanut)
- nut - (hazelnut, beech, oak acorn)
- samara - (elm, ash, maple key)
- schizocarp - (carrot)
- silique - (Radish)
Fruits in which part or all of the pericarp (fruit wall) is fleshy at maturity are simple fleshy fruits. Types of fleshy, simple fruits (with examples) are:
- berry - (tomato, avocado)
- drupe - (plum, cherry, peach, olive)
- false berry - accessory fruits (banana, cranberry)
- pome - accessory fruits (apple, pear)
An aggregate fruit develops from a flower with numerous simple pistils. An example is the raspberry, whose simple fruits are termed drupelets because each is like a small drupe attached to the receptacle. In some bramble fruits (such as blackberry) the receptacle is elongate and part of the ripe fruit, making the blackberry an aggregate-accessory fruit. The strawberry is also an aggregate-accessory fruit, only one in which the seeds are contained in achenes. In all these examples, the fruit develops from a single flower with numerous pistils.
A multiple fruit is one formed from a cluster of flowers (called an inflorescence). Each flower produces a fruit, but these mature into a single mass. Examples are the pineapple, edible fig, mulberry, osage-orange, and breadfruit.
In the photograph on the right, stages of flowering and fruit development in the noni or Indian mulberry (Morinda citrifolia) can be observed on a single branch. First an inflorescence of white flowers called a head is produced. After fertilization, each flower develops into a drupe, and as the drupes expand, they connate (merge) into a multiple fleshy fruit called a syncarp.
Fruits are plant structures whose modifications appear largely to relate to dissemination (called dispersal) of the seeds they contain.
Some fruits have coats covered with spikes or hooked burrs, either to prevent themselves from being eaten by animals or to stick to the hairs of animals, using them as dispersal agents. Other fruits are elongated and flattened out naturally and so become thin like wings or helicopter blades. This is an evolutionary mechanism to increase dispersal distance away from the parent.
Many fruits, including fleshy fruits like apple and mango, and nuts like walnut, are commercially valuable as human food, eaten both fresh and made into jams, marmalade and other preserves for future consumption.
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