Fruit and Seed
Table of Contents
FRUIT:
- A ripened ovary is called fruit. It may be of following types:
Dry:
This may be divided into three categories:
Achenial:
These are dry, one seed and indehiscent
Achene:
Single seed with membranous pericarp eg buttercup
Caryopsis:
Achene in which pericarp and testa fused eg wheat, maize, etc.
Nut:
Pericarp hard, woody forming shell as in oak
Smara:
Achene in which pericarp develops membranous outgrowth on wing eg elm
Cypsella:
Develops from bicarpellary syncarpous pistil with an inferior ovary.
Capsular:
Legume:
Develops from monocarpellary ovary + unilocular. It dehisces along both side eg pea, bean, etc
Follicle:
legume type but open at one side.
Siliqua:
Develops from bicarpellary, syncarpous pistil, having two parietal placentae as in mustard, turnip, etc.
Silicula:
Siliqua but short and less seed
Capsule:
Develops from polycarpellary, a syncarpous pistil with a superior ovary eg poppy, etc.
Succulent:
Drupe:
They are derived from monocarpellary pistil with superior ovary + one seeded as in mango, peach, etc.
Berries:
They are indehiscent, many seeded, fleshy or pulpy, as in tomato, oranges, etc.
Pome:
They develop from a syncarpous pistil with bilocular or multilocular inferior ovary eg apple.
Fruit Structure
This depiction of a cherry sliced in half illustrates the basic, three-layer structure shared by all fruits. The cherry’s skin is the outermost layer, called the exocarp. It encloses and protects two inner layers: the juicy pulp, or mesocarp, and the pit, or endocarp. Together, these three layers comprise the pericarp, the thickened wall of fruit that encases and protects the seed.
SEED:
- The ripened ovule is called a seed.
Monocot:
Seed with an embryo of single cotyledon.
Dicot:
Seed with two cotyledons
Endospermic (Albuminous):
Seed with nutritive tissue
Non-Endospermic (Exalbuminous):
Seed with lost endosperm at maturity
FRUIT AND SEED DISPERSAL:
- The following figure illustrates the dispersal agents and the examples:
Seed dispersal
Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth. As a result, plants have evolved many ways to disperse their offspring by dispersing their seeds (see also vegetative reproduction). A seed must somehow “arrive” at a location and be there at a time favorable for germination and growth. When the fruits open and release their seeds in a regular way, it is called dehiscent, which is often distinctive for related groups of plants, these fruits include; Capsules, follicles, legumes, silicles and siliques. When fruits do not open and release their seeds in a regular fashion they are called indehiscent, which include the fruits achenes, caryopsis, nuts, samaras, and utricles.
Seed dispersal is seen most obviously in fruits; however many seeds aid in their own dispersal. Some kinds of seeds are dispersed while still inside a fruit or cone, which later opens or disintegrates to release the seeds. Other seeds are expelled or released from the fruit prior to dispersal. For example, milkweeds produce a fruit type, known as a follicle, that splits open along one side to release the seeds. Iriscapsules split into three “valves” to release their seeds.
By wind (anemochory)
Dandelion seeds (achenes) can be carried long distances by the wind.
The seed pod of milkweed(Asclepias syriaca)
- Many seeds (e.g.maple, pine) have a wing that aids in wind dispersal.
- The dustlike seeds of orchids are carried efficiently by the wind.
- Some seeds, (e.g.dandelion, milkweed, poplar) have hairs that aid in wind dispersal.
Some winged seeds have two, and some have only one wing.
By water (hydrochory)
- Some plants, such as mucuna and Dioclea, produce buoyant seeds termed sea-beans or drift seeds because they float in rivers to the oceans and wash up on beaches.
By animals (zoochory)
- Seeds (burrs) with barbs or hooks (e.g.acaena, burdock, dock) which attach to animal fur or feathers, and then drop off later.
- Seeds with a fleshy covering (e.g.apple, cherry, juniper) are eaten by animals (birds,mammals, reptiles, fish) which then disperse these seeds in their droppings.
- Seeds (nuts) which are an attractive long-term storable food resource for animals (e.g.acorns, hazelnut,walnut); the seeds are stored some distance from the parent plant, and some escape being eaten if the animal forgets them.
Myrmecochory
It is the dispersal of seeds by ants. Foraging ants disperse seeds which have appendages called elaiosomes(e.g. bloodroot, trilliums, Acacias, and many species of Proteaceae). Elaiosomes are soft, fleshy structures that contain nutrients for animals that eat them. The ants carry such seeds back to their nest, where the elaiosomes are eaten. The remainder of the seed, which is hard and inedible to the ants, then germinates either within the nest or at a removal site where the seed has been discarded by the ants.[15] This dispersal relationship is an example of mutualism, since the plants depend upon the ants to disperse seeds, while the ants depend upon the plants seeds for food. As a result, a drop in numbers of one partner can reduce success of the other. In South Africa, the Argentine ant (Linepithema humile) hasinvaded and displaced native species of ants. Unlike the native ant species, Argentine ants do not collect the seeds of Mimetes cucullatus or eat the elaiosomes. In areas where these ants have invaded, the numbers of Mimetes seedlings have dropped.
FLORAL DIAGRAM AND FORMULA:
SYMBOLS USED IN FLORAL FORMULA:
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