The various modes by which plants reproduce are of three types:
In asexual and vegetative mode of reproduction, offsprings are produced from a vegetative unit formed by a parent without any fusion of gametes or sex cells. A single parent is involved and offsprings are genetically identical to the parent.
Vegetative reproduction is of the following types:
(i) Vegetative reproduction: It involves formation of new plantlets from vegetative (somatic) cell, buds or organs of the plant. Here, a vegetative part of the plant (Root, stem, leaf or bud) gets detached from the parent body and grows into an independent plant. It is similar to asexual reproduciton in that it also requires only mitotic division, no gametic fusion is involved, and newly-formed plants are genetic clones of the parent plant.
(ii) Fragmentation: In filamentous algae, an accidental breaking of the filament into many fragments, each fragment having at least one cell, may give rise to a new filament of the algae by cell division. For example, Spirogyra.
(iii) Fission: It Occurs in unicellular organisms like bacteria and yeasts where the content of the parent cell divides into 2, 4 or 8 daughter cells and accordingly the fission is known as binary or multiple fission. Each newly formed daughter cell grows into a new organism.
(iv) Budding: It also occurs in unicellular plants. A bud-like outgrowth is formed on one side of the parent cell and soon it separates and grows into a new individual. For example, in yeast.
Asexual reproduction takes place by asexual spores which may be flagellate or non-flagellate.
Spore formation: In lower plants including bryophytes and pteridophytes, special reproductive units develop asexually on the parent body. These are called spores. They are microscopic and covered by a protective wall.
When they reach the suitable environment they develop into a new plant body. For example, in bread moulds, moss, fern. In higher plants like pea, maize and gymnosperms, asexual reproduction is always heterosporous. Here, spores are produced after meiosis.
The small male spores called microspores give rise to male gametophyte. The large female spores are called megaspores, and they give rise to female gametophytes.
Sexual reproduction involves fusion of male and female reproductive cells (gametes) which are haploid and are produced by male and female reproductive organs. This fusion is known as fertilization and results in the production of a zygote (diploid). Further development of zygote gives rise to a new individual which is diploid.