Botany and Plant Science

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Hydrilla is an aquatic plant. Function of roots is to fix the plant in the soil and to absorb water from the soil. Both these requirements get reduced in aquatic plants. So, hydrilla has got poorly-developed roots. Its function is to hold the plant in its place against the water currents.

When a flower can be divided into two equal radial halves in any radial plane passing through the centre, it is said to be actinomorphic (radial symmetry), e.g. mustard, datura, chilli.

The first part of a plant to grow is the root like a straw, transports water through plant raises the height of flowers and leaves and brings closer to light. Leaves and flowers also grow.

Isobilateral leaves, which are flat leaves without an upper or lower surface. Ordinary (dorsiventral) plant leaves have an upper, harder surface which faces the sun, and a lower shade-surface where most of the carbon dioxide and water vapour exchange takes place. Isobilateral leaves exchange carbon and water equally through both surfaces, but at a lower rate than dorsiventral leaves.

The vascular bundles are found scattered throughout the ground tissue. The vascular bundles occurring nearer the ring of the stem are smaller and are closer to one another. The vascular bundles contain no cambium and consequently secondary thickening does not occur.

Some orchids like Vandas are epiphytic and grow on trees without hurting them. The orchids derive moisture and nutrients from the air and rain with their aerial roots that can be a few yards long. Older roots have a spongy outer layer called a velamen that can absorb moisture in the air and make it available to the plant. Some have chlorophyll so can manufacture food for the orchid.

Ferns, iris, and bent grass produce horizontal underground stems known as rhizomes. Leaves grow at one end and roots at the other. They can be fleshy like those of ferns and German iris and serve as important storage organs for the plant. Rhizomes are often used to propagate plants.

The pith occupies the large central part of the stem. It consists of thin-walled parenchyma cells with intercellular air spaces. Between each vascular bundle is a band of parenchyma, the medullary rays, continuous with the cortex and the pith. Functions of the Pith or Medulla: the cells of the pith store water and starch. They allow for the exchange of gases through the intercellular air spaces.

African violets and dandelions have crowns, that is compressed stems with leaves and flowers on short internodes.

A phyllode is the petiole or rachis of a leaf which is modified into a green flat structure for the purpose of photosynthesis. In such a leaf, the lamina is poorly developed. In Acacia melanoxylon, the petiole is flattened, green and becomes a phyllode. The leaflets and secondary rachii drop off.