Chapter 8 — Reproduction in Plants

Plants reproduce by two modes: asexual reproduction (new plants produced without seeds) and sexual reproduction (new plants obtained from seeds formed after fertilisation).

Vegetative propagation is a type of asexual reproduction in which new plants are produced from vegetative parts — roots, stems, leaves, and buds. Examples include rose and champa grown from stem cuttings, and potato grown from eyes (vegetative buds on the stem).

Plants produced by vegetative propagation take less time to grow and bear flowers and fruits earlier than those produced from seeds. The new plants are also exact copies of the parent plant.

Bryophyllum has buds in the margins of its leaves. If a leaf falls on moist soil, each bud can give rise to a new plant.

Yeast reproduces by budding. A small bulb-like projection (bud) grows out from the yeast cell, gradually grows, and detaches to form a new yeast cell. Sometimes another bud arises from the bud, forming a chain of buds.

In fragmentation, an organism breaks up into two or more fragments and each fragment grows into a new individual. Algae such as Spirogyra reproduce by fragmentation when water and nutrients are available.

Fungi reproduce by spore formation. Spores are asexual reproductive bodies released from the sporangium that float in air. Each spore is covered by a hard protective coat to withstand unfavourable conditions such as high temperature and low humidity, and germinates into a new individual under favourable conditions. Moss and ferns also reproduce by spores.

Flowers that contain either only pistil or only stamens are called unisexual flowers (examples: corn, papaya, cucumber). Flowers that contain both stamens and pistil are called bisexual flowers (examples: mustard, rose, petunia).

Pollination is the transfer of pollen grains from the anther of a flower to the stigma. When pollen lands on the stigma of the same flower or another flower of the same plant, it is self-pollination. When pollen from one flower lands on the stigma of a flower of a different plant of the same kind, it is cross-pollination. Pollination is carried out by wind, water, and insects.

Fertilisation is the fusion of the male and female gametes to form a zygote. The zygote develops into an embryo. After fertilisation, the ovary grows into a fruit (the ripened ovary) and the ovules develop into seeds, each containing an embryo enclosed in a protective seed coat.

Seeds are dispersed by wind (winged seeds of drumstick and maple; light hairy seeds of madar and sunflower), water (spongy or fibrous coat as in coconut), animals (spiny hooked seeds such as Xanthium and Urena), and explosive action (castor and balsam). Seed dispersal prevents overcrowding and competition for sunlight, water, and minerals, and enables plants to invade new habitats.

Flowers are the reproductive parts of a plant. The stamen is the male reproductive part and the pistil is the female reproductive part. Pollen grains in the anther contain male gametes; ovules in the ovary contain the female gamete (egg).

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