BIO 206
PLANT MORPHOLOGY
LECTURE NOTES 10th WEEK
DR. AYDAN ACAR ŞAHİN
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.
10. Unlike stem, root does not include node, stomata and chloroplast
Root systems are responsible for the following functions:
• absorption of water and organic compounds;
• anchoring of the plant body to the ground; and
• storage of food and nutrients.
• When a seed germinates, the first structure to appear is the root or the radicle.
This becomes the primary root. Other roots that branch out of the primary root are called secondary roots. The growing root tip is protected by the root cap as it moves through the coarse soil. The root cap is slimy in nature to facilitate easy movement. Above the root cap is the apical meristem. In this meristematic region, cells divide continuously by mitosis to produce new cells.
In addition to mitosis, newly divided cells undergo elongation in the same
direction of root lengthening. the tissue layers and their organization within
monocot and dicot roots
• 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
• 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
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
• 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
• 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
• A uniseriate epidermis
(some of the cells of which have formed root hairs), a cortex, and vascular
cylinder are evident at low magnification (Fig. 1). At higher magnification, the exodermis consisting of tightly packed cells,
endodermis, primary
xylem, and primary phloem are evident (Fig. 2).
• Protoxylem, large mature early metaxylem vessels and very large immature late metaxylem vessels, and pith are shown in Fig. 2.
Figure 1. Transverse section of corn (Zea mays) root stained with TBO showing primary tissue organization. E = epidermis; C = cortex; VC = vascular cylinder.
Figure 2. Transverse section of corn (Zea mays) root stained with TBO viewed at higher magnification. E = epidermis; EX = exodermis; C = cortex; arrowhead =
endodermis; double arrowhead = pericycle;
X = xylem; PH = phloem; P = pith. Large immature metaxylem vessels (*) are evident.
