Morphology of Roots

What are Roots¹

Roots are the downward growth of a plant into the substrate or soil.

Roots are positively geotropic² and hydrotropic³, which means they respond positively to the stimuli form gravity and moisture.

Function of Roots⁴

Roots usually have three main functions:

1. Roots fix the plant to the soil and give mechanical support to the plant body.
2. Roots absorb water and the minerals dissolved in it from the soil and transport them to the aerial parts where they are needed.
3. At times, the root undergoes modification and performs special functions like storage, respiration, reproduction, etc.

Use of Roots⁵

Roots have are a very useful part of plains and have applications in the following:

1. Source of food and vegetables: Most of vegetables constitute roots only, i.e. radish, turnip, beet, carrot, etc. They are rich sources of vitamins or their precursors. Some of them like sweet potato and tapioca are rich in starch, and hence are consumed as food.
2. Various types of medicinally important drugs are obtained from roots.

Organization of Root Systems

Roots systems need a lot of surface area to absorb water and minerals, to achieve this, roots grow lateral roots or branch roots⁶ that spread out to the sides.

These branch roots grow from the taproot⁷, the largest root of the plant; which developed from the embryonic root called the radicle⁸.

Branch roots may also grow branch roots, further expanding the surface area of the roots. In perennial woody plants⁹, the roots develop secondary growths such as wood and bark.

Most monocots¹⁰ and some dicots¹¹ have a mass of similarly sized roots consisting of a system of fibrous roots; caused by the death of the radicle immediately after germination¹².

As the plant ages it develops new sets of roots on stem tissue; because they don’t originate from the radicle, they are called adventitious roots¹³.

Dicots with taproot systems tend to grow and develop more than monocots with fibrous root systems. Dicots tend to grow both vertically and laterally, gaining increased conduction through the increase in root size. Monocots, on the other hand, do not grow after their initial set of roots and vascular bundles have set, causing a halt in growth.

Parts of an Underground Root

The typical underground roots usually are composed of the following parts:

• root cap,
• region of cell division,
• region of elongation,
• region of root hairs, and
• region of maturation

Root Cap¹⁴

The root caps are the tips of the root that protects the the delicate parts of the root and allows it to grow safely.

Region of Cell Division¹⁵

The region of cell division is the layer directly after the root cap, this is where meristematic tissue producing new cells.

Region of Elongation¹⁶

The region of elongation is where the new cells from the region of cell division goes and elongate, increasing the length of the roots.

Region of Root Hairs¹⁷

The region of root hairs is where elongated root cells grow root hairs¹⁸, unicellular, tubular, outgrowths formed. They strengthen the hold of the root on the soil.

Region of Maturation¹⁹

The region of maturation is the region above all other regions. Tissue here no longer absorbs anything, but it is responsible for handling the materials absorbed.

This is where lateral roots grow out of.

Types of Roots

In root systems, there are two major types:

• tap root systems
• adventitious root systems

Tap Root System²⁰

Tap root systems consist of a radicle that grows into the soil, forming a main axis of the root called the tap root. This system grows in a vertical or acropetal²¹ manner known as secondary roots, which branches into tertiary roots.

Adventitious Root System[^adventitiousrootsystem]

The roots that develop from parts other than the radicle are deemed adventitious roots. They may develop from root base notes or as internodes.

Root Modification

Modification for Food Storage²²

These types of modifications involve the roots storing carbohydrates for an extended period of time.

Tap roots gain this modification in three types²³

• Conical root
• Fusiform root
• Napiform root

Adventitious roots assume four types²⁴

• Tuberous roots
• Fasciculated tuberous roots
• Palmated tuberous rots
• Annulated roots

Modification for Support²⁵

Root modification for support is the development of aerial roots or non ground roots to provide support for the plant body.

Support modifications usually manifest in three forms:

• Clinging or climbing roots²⁶
• Stilt roots²⁷
• Columnar roots²⁸

Modifications for Special Functions[^modificationspecial]

These root modifications have unique and diverse purposes.

Pneumatophores²⁹

Pneumatophores or respiratory roots re roots grow in marshy places on seashores. These roots grow against gravity and form lenticels which allows the roots to respirate.

Haustoria

Haustoria or sucking roots are a type of parasitic root modification that allows the roots to suck nutrients from a host.

Photosynthetic Roots[^photosyntheticroots]

Photosynthetic roots are present in leafless plants and are green in color to allow the process of photosynthesis.

Epiphytic Roots³⁰

Epiphytic roots or assimilatory roots are roots which grows on branches of other plants, these are from non parasitic symbiotic plants.

Epiphytic Clinging Roots[^epiphyticclinging]

Epiphytic clinging roots are roots that cling to the host.

Epiphytic Aerial Roots³¹

Epiphytic aerial roots are roots that hang freely in the air; they absorb air and photosynthesize.

Root Tubercles³²

Root tubercles or nodulated roots are formed by having nitrogen fixing bacteria get carbohydrates from the plants.

Feeding the bacteria, while maintaining the nitrogen for the plants.

Footnotes

1. Roots are the downward growths of plants; ↩

2. Geotropism is the response to gravity; in plants, a positive response means it grows in the direction of gravity. ↩

3. Hydrotropism is the response to water; in plants a positive response means it grows in the direction of water ↩

4. The function of roots is to fix the plant to the soil and give support; absorbs water and minerals; and gained modifications to adapt to the environment. ↩

5. Roots are used as a food source and medicine through root derived drugs. ↩

6. Branch roots or lateral roots form and develop laterally; grows side to side; ↩

7. The taproot is the largest root of the plants where the initial branch roots grow; grows from the radicle. ↩

8. The radicle is the embryonic root. ↩

9. In perennial and woody plants, roots undergo a secondary growth of wood and bark. ↩

10. Monocots are plants with one seed leaf; less complex plants. ↩

11. Dicots are plants with two seed leaves; more complex plants. ↩

12. Germination is the process of a seed growing into a seedling. ↩

13. Adventitious roots originate from stem tissue and not the radicle. ↩

14. Root caps protects the delicate and growing parts of the roots. ↩

15. The region of cell division is right after the root cap and hosts meristematic tissue; new cells are produced here. ↩

16. The region of elongation is were new cells go elongate and increase the length of the roots. ↩

17. The region of root hairs is where elongated cells grow root hairs. ↩

18. root hairs are unicellular, tubular, outgrowths that form from the roots; they help the root hold on soil. ↩

19. The region of maturation is where lateral roots grow; tissue here no longer absorbs, but it still handles the absorbed material. ↩

20. Tap root systems consist of a radicle that develops a tap root; grows in an acropetal manner or towards the soil. ↩

21. acropetel growth means vertical or upwards from the base. ↩

22. Food storage modification is the roots adapting to store carbohydrates for a long time. ↩

23. Food storage modification in tap roots are conical, fusiform, or napiform. ↩

24. Food storage modification in adventitious roots are tuberous, fasciculated tuberous, palmated, or annulated. ↩

25. Support modification is the roots developing aerial roots to support the plant body. ↩

26. Clinging roots are support modifications that allow a plant to climb or cling alongside a surface. ↩

27. Stilt roots are support modifications that grow directly or obliquely downward and penetrate into the soil to give additional support. ↩

28. Columnar roots are support modifications that involves roots growing downward pillars that provide support. ↩

29. Pneumatophores or respiratory roots, are upward growing roots that allow the plant to respirate. ↩

30. Epiphytic roots or assimilatory roots are roots which attach on the branches of other plants without stealing nutrients. ↩

31. Epiphytic aerial roots are roots that hang freely in the air that absorb air and photosynthesize. ↩

32. Root tubercles are roots that host nitrogen fixing bacteria that takes carbohydrates from the plant. ↩