Class 7 Science Reproduction in Plants Notes

Vegetative Reproduction

Like spores, higher plants can also survive unfavourable conditions. Under such conditions, the aerial parts of a plant usually die but the underground parts like root or stem remain dormant or inactive. When conditions are favourable again, these dormant parts grow again to produce a new plant. Similar is the case with Colocasia, sweet potato, potato etc., which do not produce any seeds. Man has encashed this property of such plants to maximum advantage. Thus, when new plants are produced from parts of the parent plant such as the root, stem or leaves, without the help of any reproductive organs, it is known as vegetative reproduction. Different methods are used in horticulture for fruit yielding and ornamental plant, like, cutting (stem), eg. in sugar cane, layering and grafting in mango, roses etc.

a) Vegetative reproduction by stem: Some plants send out a side branch from the main plant, and a root grows down into the soil. The stem grows in length and creeps along the ground (runners) and forms roots at intervals, thus forming new plants (Fig.8). When the new plant has grown enough, the link between the old and the new plant withers away, eg. some species of grass and strawberry.

Some plants reproduce vegetatively beneath the soil, e.g., onion, potato, ginger, Colocasia etc., Modified underground stems also store food. Underground stems are capable of producing several new plants from their buds and thus help the plant to multiply. Tuber, bulb, corn, rhizome are the different modifications of an underground stem. (Fig,8).

i) Tuber: Seeds of potato are not viable. Potato tuber is the swelling of the branch of an underground stem. The leaves on the branches and stems growing above the soil make food in the form of starch. This starch is passed down the stem via the phloem tissues, into the underground branches to make new tuber The tubers have ‘eyes’ present on the them. The ‘eye’ is made up of a bud and scale leaves. When sown, each eye is capable of developing the root stem and leaves, as it contains meristematic tissue.

ii) Bulb: Bulbs are actually swollen large underground buds covered with scale leave It is a shoot modification that has a very short stem and apical and axillary buds. It stores food for the growth of new leaves and flowers. For example, onion, lily, tulip, garlic etc.

iii) Rhizome: It is horizontally growing underground stem, swollen with stored food. A rhizome bears distinct nodes, internodes scaly leaves and adventitious roots. It has buds on its surface from which grow new plants. Ginger and turmeric are examples (Fig.9).

iv) Corm: Some plants like Colocasia, Crocus, Gladiolus etc., consist of a short swollen solid fleshy underground stem (Fig. 10). It is in fact a condensed form of rhizome and bears one or more bud The food made by the leaves is stored in the corm at the end of the growing season, until it is used for the growth of a new plant, the following season. Daughter corms develop from the sides of the parent corm, which later break off to form new plants.