D. Inflorescence

Definition of Inflorescence: A specialized axis or branch over which flowers are produced or borne in definite manner

Structure Parts:

• Peduncle: Main axis
• Flowers: Borne on peduncle

Significance

• Not all flowers mature at same time
• Advantages:
• Increases chances of pollination
• Large number of flowers can be pollinated in single visit
• Makes plant attractive

Types of Inflorescence

Racemose Type

• Growth of peduncle: Infinite or unlimited
• Apical bud: Free for continuous growth
• Flower arrangement:
• Older flowers at base
• Borne in acropetal succession
• Order of opening is centripetal when peduncle is disc-shaped

Cymose Type

• Growth of peduncle: Finite or limited
• Apical meristem: Terminates into flower
• Flower arrangement:
• Oldest flower at apex
• Borne in basipetal succession
• Order of opening is centrifugal if peduncle is compressed from top

---

E. Flower

Flower:

A highly modified and condensed shoot meant for sexual reproduction

Position

A flower can be:

• Axillary - (borne in leaf axil)

• Terminal (at tip of main axis)

Structure

Thalamus (Receptacle)

• Consists of four compactly arranged nodes and three highly condensed internodes

• From each node, a circle or whorl of modified leaves is produced

• Color: Green (can perform photosynthesis)

Floral Terminology

 

---

Insertion of Floral Whorls

Definition: Position and arrangement of floral whorls with respect to gynoecium on thalamus

Hypogyny

• Ovary position: Highest position
• Other parts: Below ovary
• Ovary nature: Superior
• Flower type: Hypogynous
• Floral formula symbol:

   

  

• Examples: Brinjal, Mustard, China rose

Perigyny

• Positions: Ovary and other floral parts occupy about same position
• Thalamus shape: Cup-shaped or saucer-shaped
• Ovary nature: Semi-superior or semi-inferior
• Arrangement: All floral whorls at rim of thalamus
• Flower type: Perigynous
• Floral formula symbol:

   

  

• Examples: Rose, Pea, Bean

Epigyny

• Thalamus shape: Closed cup-like
• Ovary enclosure: Completely encloses ovary (may fuse with ovary wall)
• Other parts: Occupy superior position
• Ovary nature: Inferior
• Flower type: Epigynous
• Floral formula symbol:

   

  

• Examples: Sunflower, Guava

---

Floral Parts and Their Structure

Thalamus (Torus/Receptacle)

• Called torus or receptacle
• Green in color (can perform photosynthesis)

Calyx (K)

Structure:

• Outermost floral whorl
• Members: Sepals
• Usually green in color (perform photosynthesis)

Types:

• Gamosepalous: Sepals united (e.g., China rose)
• Polysepalous: Sepals free (e.g., Brassica)

Function

• Protect inner floral parts in bud condition
• Modify into pappus (stiff, hairy structures) for wind dispersal (e.g., Tridax, Sonchus)

Corolla (C)

Structure:

• Second floral whorl
• Members: Petals (variously colored)

Types:

• Polypetalous: Petals free (e.g., Rose)
• Gamopetalous: Petals fused (e.g., Datura)

Function:

• Attract different agencies for pollination

Perianth (P)

Definition: Calyx and corolla remain undifferentiated

• Members: Tepals

Types:

• Polyphyllous: Tepals free
• Gamophyllous: Tepals fused

Sub-types:

• Sepaloid perianth: Green tepals
• Petaloid perianth: Brightly colored tepals (e.g., Lily)

 

Aestivation (Arrangement in Bud)

Definition: Mode of arrangement of sepals, petals, or tepals in flower bud with respect to members of same whorl

Types:

Valvate

• Margins remain in contact or lie close
• Do not overlap
• Example: Calyx of Datura

Twisted (Contorted)

• One margin of a member is overlapped
• Other margin overlaps adjacent member
• Example: Corolla of China rose

Imbricate

• One member internal (overlapped at both margins)
• One member external (completely outside)
• Rest overlap and get overlapped
• Example: Calyx of Cassia

Vexillary

• Corolla butterfly-shaped (5 petals)
• Vexillum: Outermost and largest
• Wings: Two lateral petals
• Keel: Two smallest inner, fused petals
• Example: Corolla of Pisum sativum

Epicalyx

• Additional whorl of sepal-like structures
• Formed by bractioles outside calyx

• Characteristic feature of family Malvaceae

Androecium (A)

Definition: Third floral whorl (male reproductive part)

• Members: Stamens

Condition: If all stamens are free = polyandrous

Stamen Parts:

Anther (terminal, produces pollen grains)

• Usually bilobed/tetralocular/tetrasporangiate(e.g., Datura)

• Sometimes monothecous(e.g., Hibiscus)

Filament (stalk, bears anther)

Connective (connects two anther lobes to filament)

 

Cohesion (Fusion within same whorl):

Adelphy

• Stamens united by filaments
• Anthers free

Syngeny

• Anthers united
• Filaments free
• Example: Sunflower

Synandrous

• Fused by both filaments and anthers
• Example: Cucurbita

 

Adhesion - (Fusion between different whorls):

Epipetalous

• Stamens united with petals
• Example: Datura

Epiphyllous

• United with tepals
• Example: Lily

 

Gynoecium (G)

Definition: Innermost floral whorl (female reproductive part/pistil)

• Members: Carpels

Types:

• Syncarpous: Carpels fused
• Apocarpous: Carpels free

Carpel Parts:

Stigma

• Terminal part
• Receives pollen grains

Style

• Narrow structure
• Connects ovary with stigma

Ovary

• Basal, swollen, fertile part
• Produces ovules on placenta

Placentation (Arrangement of Ovules on Placenta)

Marginal

• Ovules placed on fused margins of unilocular ovary

• Examples: Pea, Bean

Axile

• Ovules placed oncentral axis of multi-locular ovary

• Examples: China rose, Cotton

Parietal

• Ovules placed on inner wall of unilocular ovary of multicarpellary syncarpous gynoecium

• Examples: Papaya, Cucumber

Basal

• Single ovule at base of unilocular ovary
• Examples: Sunflower, Rice, Wheat

Free Central

• Ovules borne on central axis not attached to ovary wall

• Examples: Argemone, Dianthus, Celosia

---

Table 1: Androecium - Structure and Fusion Patterns

 

---

Table 2: Gynoecium - Structure and Components

 

---

Table 3: Placentation - Types and Ovule Arrangement