Study and identification of different types of inflorescence (cymose and racemose)

Aim Of The Experiment

To study and identify different types of Inflorescences(racemose/cyme).

Theory

In angiosperms, the flowers are either borne singly or clusters. Flowers that are borne individually are by themselves, solitary whereas the flowers that are produced in a group or a cluster on a shared stalk or peduncle go on to form an inflorescence.

What is inflorescence?

In a flowering plant, the inflorescence is a cluster of flowers seen on a branch or branches. On the basis of flower arrangement on the peduncle(main axis) and flower timing (indeterminate and determinate), inflorescence can be classified into the following:

Racemose type

• • Simple raceme – The pedicellate bisexual flowers are arranged in an acropetal succession on an elongated peduncle. Example – Crotalaria
  • Spike – Similar to simple raceme except that the flowers are sessile.Example – Achyranthes
  • Compound Spadix – Unisexual male and female flowers sessile flowers are arranged in acropetal succession. Example – Cocos nucifera
  • Capitulum – Inflorescence axis is flattened to form a receptacle wherein ligulate ray florets and tubular disc florets develop in a centripetal manner. Example – Tridax

Cyme type

• • Solitary cyme – The Peduncle ends up in a flower. Example – Hibiscus
  • Helicoid cyme – Flowers are consecutively produced on one side on the peduncle to give a helicoid appearance. Example – Hamelia
  • Dichasial – The peduncle ends up with a flower and two lateral flowers are produced under the central flower one on each side for a cluster of three flowers to be formed. Example – Jasminum.
  • Polychasial cyme- Same pattern of development of flowers as seen in dichasial additionally it is continued here. Centrifugal mode of development. Example – Calotropis

Special Types

• Cyathium – Inflorescence is protected by an involucre of five bracts wherein a nectary gland is connected to it. One female achlamydeous flower centrally with a long pedicel bringing the ovary out of the involucral cup. Male flowers are achlamydeous, found in 5 bundles corresponding to 5 bracts. Example: Euphorbia geniculata
• Hypanthodium – Inflorescence is pear-shaped with an opening at the tip known as Ostiole causing a cavity inside. Example: Ficus

Materials Required

• Inflorescence of any plant locally available
• Hand lens
• Water
• Beaker

Procedure Of The Experiment

• Pick some inflorescences of locally available plants
• Place them in a beaker
• Make yourself familiar with the types and characteristics of different inflorescences
• Sort the inflorescences into cymose and racemose
• List the different plant species in a table
• Identify the different types of inflorescence with justification
• Make a note of the location of the inflorescence in the plant which can either be terminal or axillary.
• Sketch out labelled diagrams of the inflorescence of each of the samples collected for the experiment indicating the arrangement of the youngest and the oldest flowers on the main axis
• Sketch a diagram of a flower of every inflorescence. Label different parts after identification.
• Position of the ovary is noted corresponding to the floral parts arranged i.e., perigynous, epigynous, hypogynous.

Inference

• Inflorescence can either be of the type-indefinite or definite. Classification is based on
• Position on the mother axis i.e., terminal or axillary
• Maturity of flowers
• Number of flowers
• Inflorescence and characteristics of flowers assist in plant parts identification and taxonomic classification
• Observe the inflorescence type that is common in the locally available plants.

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Further Reading