Types of leaf :
- A leaf is said to be simple, when its lamina is entire or when incised, the incisions do not touch the midrib.
- When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is called compound.
- Bud present in the axil of petiole in both simple and compound leaf.
- Bud never present in the axil of the leaflets of compound leaf.
- Pinnately compound leaf: number of leaflets present in a common axis called rachis, which represents the midrib of leaf.
- Palmately compound leaves: leaflets are attached to the common point i.e. at the top of the petiole.
Phyllotaxy :
- It is the pattern of arrangement of leaves on the stem of branch.
- Alternate : a single leaf arises from each node
- Opposite : a pair of leaves arise at each node and lie opposite to each other.
- Whorled : more than two leaves arise at a node and form a whorl.
Modifications of leaves : leaves are often modified to perform functions other than photosynthesis.
- Modified to tendril for climbing as in peas.
- Modified to spines for defense as in cacti.
- Fleshy leaves of onion store food.
- In Australian acacia, the leaves are small the short-lived. The petioles expanded, become green and synthesize food.
- In insectivorous plant leaves are modified to trap insects e.g. pitcher plant, Venus fly trap.
THE INFLORESCENCE : The arrangement of flowers on the floral axis of stem.
- A flower is a modified shoot –
- Apical meristem changes to floral meristem.
- Internodes do not elongate and the axis gets condensed.
- The apex produces different kinds of floral appendages laterally at successive nodes instead of leaves.
- Racemose : the main axis continues to grow; the flowers are borne laterally in an acropetal succession.
- Cymose : the main axis terminates in flower, hence limited to grow. The flowers are borne in a basipetal order.
THE FLOWER :
- Atypical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel called thalamus or receptacle.
- Calyx, corolla, Androecium and Gynoecium.
- Calyx and corolla are accessory organs.
- Androecium and Gynoecium are reproductive organs.
- In flower like lily, the calyx and corolla are indistinct and are called perianth.
- Bisexual: flower having both Androecium and Gynoecium.
- Unisexual: flower having either stamens or carpel.
Symmetry :
- Actinomorphic: radially symmetrical.
- Zygomorphic: bilaterally symmetrical.
- Asymmetrical: when a flower cannot be divided into two equal half in any plane.
Pattern of flower :
- A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5 respectively.
- Reduced leaf found at the base of the pedicel are called bract.
- Flowers which bears bract are said to be bracteates.
- Flowers without bract are said to be ebracteate.
Position of floral parts on thalamus :
- Hypogynous :
- Gynoecium occupies the highest position.
- Other whorls are present below the Gynoecium.
- Ovary is said to be superior. E.g. mustard, China rose and brinjal.
- Epigynous :
- The thalamus encloses the ovary.
- Thalamus fused with ovary.
- The other whorl arises above the ovary.
- Ovary is inferior. E.g. guava, cucumber, ray florets of sunflower.
- Perigynous :
- Ovary is said to be half inferior.
- The Gynoecium situated in the centre.
- Other whorls located on the rim of the thalamus almost at the same level. E.g. plum, Rose, peach.
