The Physiology of Roots

Roots perform four functions in the life of the plants, they are the foundation on which the plant grows, providing stability against winds, and of course they supply the plant with the water and chemicals it needs to produce sap, and hence feed the plant.In many annual plants they act as a storage for energy allowing the plant to 'hibernate' below ground over winter. Many plants reproduce by growing small bulblets.

All plants have a major root that grows down into the soil. This is the taproot and provides the main anchorage to the ground.

The roots spread out about as far as the plant is wide, adding to the stability of the plant.

They also provide the plant with the resources it needs to grow. This can require a massive root structure and you can usually assume that what you see of the plant above ground, is echoed in volume below ground.

The roots themselves are a complex structure, as we will see in this section.

As with all parts of the plant, the veins of the xylem and phloem are present in the roots. They are however in bundles, rather than the rings of the upper parts of the plant.

The root hairs perform two functions. Firstly they massively increase the roots surface area, increasing its ability to absorb water and chemicals.

Secondly their travels out into the surrounding soil, make a better anchorage for the root to move forward and further fix the plant into the ground.

Should the roots be allowed to dry out, either while repotting, or through under watering, the root hairs will die. This will significantly reduce the plants ability to take up water and hence delay its recovery.

The cells of the region of maturity were formed by the ageing of cells in the region of elongation. This region is often referred to as the 'Region of differentiation', implying that as the cells mature, they become different, some developing into root hairs, some forming the vascular tissue and others may form the beginnings of root buds and hence new roots.

The region of elongation contains cells recently produced by the meristematic cells behind the root cap. These cells continue to expand pushing the root tip forward. As these cells age they join the region of maturity.

The meristematic zone is where the roots growth takes place.

The cells of the meristematic zone are constantly dividing, with those older cells, towards the back of the zone rapidly elongating, this elongation pushes the root cap forward. Those cells at the front of the zone replacing damaged cells of the root cap.

The root cap could be described as the 'Crash helmet' of the root. It protects the meristematic zone, while shedding cells to lubricate the roots passage through the soil.

The root cap is sensitive to the earth's gravity and it is this sensitivity that ensures the roots primarily grow downward into the soil. This sensitivity is called geotropism

Categories of bulbs

The plants we loosely call bulbs are in fact divided into four broad categories: true bulbs, corms, tubers/tuberous roots and rhizomes.

A true bulb such as a tulip or daffodil is almost a complete embryo of the plant to come, packed inside a covering of fleshy scales or layers that store the plantís food.

A corm, such as crocus or gladiolus, is a solid mass of storage tissue with a basal plate below and buds, sometimes called eyes, on top.

A tuber, such as a fancy leafed calladium or calla lily, is also a solid mass of storage tissue with buds but no basal plate. A tuberous rooted plant such as the dahlia, has swollen, food-storing roots; the bud eyes are not on the roots but on the base of the plantís stem.

A rhizome, such as canna, is a thickened underground stem that grows horizontally, with bud eyes on top and roots below.

ģ Allen. C. Roffey 17:15 03/02/2003