Primary Root Anatomy: Monocot and Dicot Root Systems, Slides of Biology

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Primary Root Anatomy

DİCOT and MONOCOT

ROOT

Dr.Arzu Gürsoy Ergen Arş.Gör Duygu Berdi

Morphology of root characteristics:

1. Root is defined as the descending part of the plant axis.
2. It is positively geotropic.
3. It is positively hydrotropic
4. It is negatively phototropic.
5. It develops from the radicle of the embryo during seed germination.
6. Roots are generally non green and cylindrical.
7. They produce only similar organs i.e. secondary and tertiary roots
8. They do not show nodes and internodes.
9. The first true roots are found in members of Spermatophyta. 1 0. Unlike stem, root does not include node, stomata and chloroplast

 A root that develops from any other part other than the radicle is known as adventitious root. Such roots may develop from the base of the stem, nodes or from leaves.  In monocots, radicle is short lived and from the base of the stem a thick cluster of all equal sized roots arises. This is known as the adventitious root system e.g. Maize, wheat, sugarcane, etc.  It is also known as fibrous root system as the adventitious roots of grasses (monocots) look like fibres. Fibrous roots do not grow very deep into the soil  The main root is called primary root. Its branches of first order are called secondary roots and branches of secondary order are called tertiary roots and so on.  The main root along with its branches forms a tap root system e.g. Mustard (Brassica), Sunflower (Helianthus) etc.  Presence of a tap root system is a characteristic feature of dicotyledonous plants. The tap root normally grows vertically downwards to a lesser or greater depth, while secondary and tertiary roots grow obliquely downwards or some grow horizontally outwards

Monocot vs. Dicot Subject: Primary root anatomy Sub tobic: Monocotyledone root Fam: Iridaceae Sp.: Iris sp. Sec.dir: transversal section from the young root Subject: Primary root anatomy Sub tobic: Dicotyledone root Fam: Ranunculaceae Sp.: Ranunculus aquatilis Sec.dir: transversal section from the young root/Ready preparation

 A higher magnification of the vascular cylinder shows the tetrarch arrangement (i.e., four protoxylem poles) of primary xylem with alternating regions of primary phloem, the pericycle , endodermis , and parenchyma cells in the cortex

Dicot

Monocot

Secondary Growth in Dicot Roots

UNDERGROUND AERIAL

Tap Root Modifications

(for storage of food)

Conical

Fusiform Napiform

In some plants the tap roots store reserve food for which they become swollen and assume different shapes. There are three types: Fusiform Napiform Conical

Adventitious Root Modifications

1. Tuberous or tubercular root : , e.g., Ipomoea batotas (Sweet potato )

Here, the modified adventitious root is swollen without any definite shape. It is always produced singly and not in clusters.

2. Fasciculated roots e.g., Asparagus, Dahlia

In Dahlia and Asparagus a number of adventitious roots arise as a cluster, from almost the same level at the base of the stem.

5. Annulated roots e.g., Ipecac. Here, the adventitious roots have series of ring-like

swelling on their surface.

Aerial Root Modifications

Aerial roots are adventitious roots which develop from the aerial parts

of the plant to perform various functions.

A) For mechanical support

Prop roots

Stilt roots

Climbing root

B) For vital functions

Haustoria or sucking roots

Respiratory roots or breathing roots or pneumtophores

Floating roots

Epiphtic roots