Reproduction means producing offspring for the survival of the species. Plant reproduction is the production of new individuals or offspring in plantswhich can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametesresulting in offspring genetically different from the parent or parents.
Asexual reproduction produces new individuals without the fusion of gametes, genetically identical to the parent plants and each other, except when mutations Asexual reproduction in flowering plants pdf. In seed plantsthe offspring can be packaged in a protective seedwhich is used as an agent of dispersal. Reproduction in which male and female gametes do not fuse, as they do in sexual reproduction. Asexual reproduction may occur through buddingfragmentationAsexual reproduction in flowering plants pdfspore formation and vegetative propagation.
Plants have two main types of asexual reproduction in which new plants are produced that are genetically identical clones of the parent individual.
Vegetative reproduction invoves a vegetative piece of the original plant budding, tilleringetc. Apomixis occurs in many plant species and also in some non-plant organisms. For apomixis and similar processes in non-plant organisms, see parthenogenesis.
Natural vegetative reproduction is mostly a process found in herbaceous and woody perennial plants, and typically involves structural modifications of the stem or roots and in a few species leaves. Most plant species that employ vegetative reproduction do so as a means to perennialize the plants, allowing them to survive from one season to the next and often facilitating their expansion in size.
A plant that persists in a location through vegetative reproduction of individuals constitutes a clonal colony ; a single rametor apparent individual, of a clonal colony is genetically identical to all others in the same colony.
The distance that a plant can move during vegetative reproduction is limited, though some plants can produce ramets from branching rhizomes or stolons that cover a wide area, often in only a few growing seasons. In a sense, this process is not one of reproduction but one of survival and expansion of biomass of the individual. When an individual organism increases in size via cell multiplication and remains intact, the process is called vegetative growth.
However, in vegetative reproduction, the new plants that result are new individuals in almost every respect except genetic. A major disadvantage to vegetative reproduction, is the transmission of pathogens from parent to offspring; it is uncommon for pathogens to be transmitted from the plant to its seeds in sexual reproduction or in apomixisthough there are occasions when it occurs. Seeds generated by apomixis are a means of asexual reproduction, involving the formation and dispersal of seeds that do not originate from the fertilization of the embryos.
Hawkweed "Asexual reproduction in flowering plants pdf"dandelion Taraxacumsome Citrus Citrus and Kentucky blue grass Poa pratensis all use this form of asexual reproduction. Pseudogamy occurs in some plants that have apomictic seeds, where pollination is often needed to initiate embryo growth, though the pollen contributes no genetic material to the developing offspring.
Asexual reproduction is a type of reproduction where the offspring comes from one parent only, thus, inheriting the characteristics of the parent. A rhizome Asexual reproduction in flowering plants pdf a modified underground stem serving as an organ of vegetative reproduction; the growing tips of the rhizome can separate as new plants, e. Prostrate aerial stems, called runners or stolonsare important vegetative reproduction organs in some species, such as the strawberrynumerous grassesand some ferns.
Adventitious buds form on roots near the ground surface, on damaged stems as on the stumps of cut treesor on old roots. These develop into above-ground stems and leaves.
A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include Elm UlmusDandelion Taraxacumand many members of the Rose family such as Rosa and Rubus.
Plants like onion Allium cepahyacinth Hyacinthnarcissus Narcissus and tulips Tulipa reproduce by dividing their underground bulbs into more bulbs. Other plants like potatoes Solanum tuberosum and dahlia Dahlia reproduce by a similar method involving underground tubers. Gladioli and crocuses Crocus reproduce in a similar way with corms.
The most common form of plant reproduction utilized by people is seeds, but a number of asexual methods are utilized which are usually enhancements of natural processes, including: Asexual methods are most often used to propagate cultivars with individual desirable characteristics that do not come true from seed.
In horticulture, a "cutting" is a branch that has been cut off from a
Asexual reproduction in flowering plants pdf plant below an internode and then rooted, often with the help of a rooting liquid or powder containing hormones. When a full root has formed and leaves begin to sprout anew, the clone is a self-sufficient plant,  genetically identical to the mother plant. Examples include cuttings from the stems of blackberries Rubus occidentalisAfrican violets Saintpauliaverbenas Verbena to produce new plants.
A related use of cuttings is graftingwhere Asexual reproduction in flowering plants pdf stem or bud is joined onto a different stem. Nurseries offer for sale trees with grafted stems that can produce four or more varieties of related fruits, including apples. The most common usage of grafting is the propagation of cultivars onto already rooted plants, sometimes the rootstock is used to dwarf the plants or protect them from root damaging pathogens.
Since vegetatively propagated plants are clones, they are important tools in plant research. When a clone is grown in various conditions, differences in growth can be ascribed to environmental effects instead of genetic differences. Sexual reproduction involves two fundamental processes: In between these two processes, different types of plants and algae vary, but many of them, including all land plantsundergo alternation of generationswith two different multicellular structures phasesa gametophyte and a sporophyte.
The gametophyte is the multicellular structure plant that is haploidcontaining a single set of chromosomes in each cell. The gametophyte produces male or female gametes or bothby a process of cell division called mitosis.
The fusion of male and female gametes fertilization produces a diploid zygotewhich develops by mitotic cell divisions into a multicellular sporophyte.
The mature sporophyte produces spores by meiosissometimes referred to as " reduction division " because the chromosome pairs are separated once again to form single sets. In mosses and liverworts the gametophyte is relatively large, and the sporophyte is a much smaller structure that is never separated from the gametophyte.
In fernsgymnospermsand flowering plants angiospermsthe gametophytes are relatively small and the sporophyte is much larger. In gymnosperms and flowering plants the mega gametophyte is contained within the ovule that may develop into a seed and the micro gametophyte is contained within a pollen grain. Unlike animals, plants are immobile, and cannot seek out sexual partners for reproduction. In the evolution of early plants, abiotic means, including water and wind, transported sperm for reproduction.
The first plants were aquaticas described in the page " Evolutionary history of plants ", and released sperm freely into the water to be carried with the currents. Primitive land plants like liverworts and mosses had motile sperm that swam in a thin film of water or were splashed in water droplets from the male reproduction organs onto the female organs.
As taller and more complex plants evolved, modifications in the alternation of generations evolved; in the Paleozoic era progymnosperms reproduced by using spores dispersed on the wind. The seed plants including seed fernsconifers and cordaiteswhich were all gymnospermsevolved million years ago; they had pollen grains that contained the male gametes for protection of the sperm during the process of transfer from the male to female parts. It is believed that insects fed on the pollen, and Asexual reproduction in flowering plants pdf thus evolved to use insects to actively carry pollen from one plant to the next.
Seed producing plants, which include the angiosperms and the gymnosperms, have heteromorphic alternation of generations with large sporophytes containing much reduced gametophytes. Angiosperms have distinctive reproductive organs called flowers, with carpelsand the female gametophyte is greatly reduced to a female embryo sac, with as few as eight cells.
The male gametophyte consists of the pollen grains. The sperm of seed plants are non-motile, except for two older groups of plants, the Cycadophyta and Asexual reproduction in flowering plants pdf Ginkgophytawhich have flagellated sperm. Flowering plants are the dominant plant form on
Asexual reproduction in flowering plants pdf and they reproduce by sexual and asexual means.
Often their most distinguishing feature is their reproductive organs, commonly called flowers. Sexual reproduction in flowering plants involves the production of male and female gametesthe transfer of the male gametes to the female ovules in a process called pollination. After pollination occurs, fertilization happens and the ovules grow into seeds within a fruit. After the seeds are ready for dispersalthe fruit ripens and by various means the seeds are freed from the fruit and after varying amounts of time and under specific conditions the seeds germinate and grow into the next generation.
The anther produces male gametophytes which are pollen grainswhich attach to the stigma on top of a carpelin which the female gametophytes inside ovules are located. After the pollen
Asexual reproduction in flowering plants pdf grows through the carpel's style, the sperm from the pollen grain migrate into the ovule to fertilize the egg cell and central cell within the female gametophyte in a process termed double fertilization.
The resulting zygote develops into an embryo, while the triploid endosperm one sperm cell plus a binucleate female cell and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which produced the female gametophyte sthen grows into a fruitwhich surrounds the seed s. Plants may either self-pollinate or cross-pollinate. In plants that use insects or other animals to move pollen from one flower to the next, plants have developed greatly modified flower parts to attract pollinators and to facilitate the movement of pollen from one flower to the insect and from the insect back to the next flower.
Flowers of wind pollinated plants tend to lack petals and or sepals; typically large amounts of pollen are produced and pollination often occurs early in the growing season before leaves can interfere with the dispersal of the pollen.
Many trees and all grasses and sedges are wind pollinated, as such they have no need for large fancy flowers. Plants have a number of different means to attract pollinators including colour, scent, heat, nectar glands, edible pollen and flower shape. Along with modifications involving the above structures two other conditions play a very important role in the sexual reproduction of flowering plants, the first is timing of flowering and the other is the size or number of flowers produced.
Often plant species have a few large, very showy flowers while others produce many small flowers, often flowers are collected together into large inflorescences to maximize their visual effect, becoming more noticeable to passing pollinators.
Flowers are attraction strategies and sexual expressions are functional strategies used to produce the next generation of plants, with pollinators and plants having co-evolved, often to some extraordinary degrees, very often rendering mutual benefit. The largest family of flowering plants is "Asexual reproduction in flowering plants pdf" orchids Orchidaceaeestimated by some specialists to include up to 35, species,  which often have highly specialized flowers that attract particular insects for pollination.
The stamens are modified to produce pollen in clusters called polliniawhich become attached to insects that crawl into the flower. The flower shapes may force insects to pass by the pollen, which is "glued" to the insect. Some orchids are even more highly specialized, with flower shapes that mimic the shape of insects to attract them to 'mate' with the flowers, a few even have scents that mimic insect pheromones.