BIO BOTANY [5 Mark each]

Leaves may stay and function for few days to many years, largely determined by the adaptations to climatic conditions.

• Cauducuous (Fagacious): Falling off soon after formation, e.g., Opuntia and Cissus quadrangularis.
• Deciduous: Falling at the end of growing season so that the plant (tree or shrub) is leafless in winter / summer season, e.g., Maple, Plumeria, Launea and Erythrina.
• Evergreen: Leaves persist throughout the year, falling regularly so that tree is never leafless. e.g., Mimusops and Calophyllum.
• Marcescent: Leaves not falling but withering on the plant as in several members of Fagaceae.

Rolling or folding of individual leaves is called ptyxis. There are seven types of ptyxis as follows:

1. Reclinate – When the upper half of the leaf blade is bent upon the lower half as in loquat (Eriobotrya japonica).
2. Conduplicate – When the leaf is folded lengthwise along the mid – rib, as in guava, sweet potato and camel’s foot tree (Bauhinia).
3. Plicate or Plaited – When the leaf is repeatedly folded longitudinally along ribs in a zig – zag manner, as in Borassus flabellifer.
4. Circinate – When the leaf is rolled from the apex towards the base like the tail of a dog, as in ferns.
5. Convolute – When the leaf is rolled from one margin to the other, as in banana, aroids and Indian pennywort. Musa and members of Araceae.
6. Involute – When the two margins are rolled on the upper surface of the leaf towards the mid – rib or the centre of the leaf, as in water lily, lotus, Sandwich Island Climber (Antigonon) and Plumbago.
7. Crumpled – When the leaf is irregularly folded as in cabbage.

The mode of arrangement of leaves on the stem is known as phyllotaxy (Greek. Phyllon = leaf; taxis = arrangement). Phyllotaxy is to avoid over crowding of leaves and expose the leaves maximum to the sunlight for photosynthesis. The four main types of phyllotaxy are:

1. Alternate
2. Opposite
3. Temate and
4. Whorled.

1. Alternate phyllotaxy: In this type there is only one leaf per node and the leaves on the successive nodes are arranged alternate to each other. Spiral arrangement of leaves show vertical rows are called orthostichies. They are two types:

• Alternate spiral: In which the leaves are arranged alternatively in a spiral manner. e.g. Hibiscus and Ficus.
• Alternate distichous or Bifarious: In which the leaves are organized alternatively in two rows on either side of the stem, e.g. Monoon longifolium (Polyalthia longifolia).

2. Opposite phyllotaxy: In this type each node possess two leaves opposite to each other. They are organized in two different types:

1. Opposite superposed: The pair of leaves arranged in succession are in the same direction, that is two opposite leaves at a node lie exactly above those at the lower node. e.g. Psidium (Guava), Eugenia jambolana (Jamun) and Quisqualis (Rangoon creeper).
2. Opposite decussate: In this type of phyllotaxy one pair of leaves is placed at right angles to the next upper or lower pair of leaves, e.g., Calotropis, Zinnia and Ocimum

3. Ternate phyllotaxy: In this type there are three leaves attached at each node. e.g. Nerium.
4. Whorled (verticillate) type of phyllotaxy: In this type more than three leaves are present in a whorl at each node forming a circle or whorl, e.g. Allamanda and Alstonia scholaris.

The characteristics of leaf:

• Leaf is a lateral appendage of the stem.
• It is borne at the node of the stem.
• It is exogenous in origin.
• It has limited growth.
• It does not possess apical bud.
• It has three main parts namely, leaf base, petiole and lamina.
• Lamina of the leaf is traversed by vascular strands, called veins.

A flow chart illustrating stem modifications:

Buds are the growing points surrounded by protective scale leaves:

1. Terminal bud or Apical bud: These buds are present at the apex of the main stem and at the tips of the branches.
2. Lateral bud or Axillary bud: These buds occur in the axil of the leaves and develop into a branch or flower.
3. Extra axillary bud: These buds are formed at nodes but outside the axil of the leaf as in Solanum americanum.
4. Accessory bud: An extra bud on either side (collateral bud) or above (superposed bud or serial bud) the axillary bud. e.g: Citrus and Duranta.

The location, cellular types and the functions of different zones of root:

S.No.	Feature	Meristematic zone	Zone of elongation	Zone of maturation
1.	Position	It lies just above the root cap	It lies just above the meristematic zone	It lies above the zone of elongation.
2.	Types of cells	Meristematic cells, actively divide and continuously increase in number	Elongated cells	Mature differentiated cells
3.	Functions	This is the main growing tip of the root	The cells increase the length and cause enlargement of the root	The cells differentiate into various tissues like epidermis, cortex and vascular bundles. It also produces root hairs which absorb water and minerals from the soil

quatic plants and their environmental adaptation with an example:

Aquatic habitat
S.No.	Types	Nature of environmental adapatation	Example
1.	Free floating	Growing on water surface	Eichhornia
2.	Submerged	Plants growing completely under water	Hydrilla
3.	Emergent	Plants with roots or stems anchored to the substrate under water and aerial shoots growing above water	Limnophyton
4.	Floating leaved	Anchored at bottom but with floating leaves	Nelumbo
5.	Mangroves	Plants growing emergent in marshy saline habitat	Avicennia