Biology Today — January 2018

Functions

of Leaf

Leaves are the main seat of

transpiration.

Buoyancy in some aquatic

plants such as Eichhornia, etc.

Leaves protect the axillary and

terminal buds from mechanical

injury and desiccation.

Support, e.g., Doxantha

unguis-cati, etc.

Storage of food, e.g., succulent leaves

of xerophytic plants such as Aloe, etc.

Protection from grazing animals and

transpiration, e.g., Opuntia, etc.

Reproduction, e.g., Bryophyllum.

Nitrogen nutrition in insectivorous plants

such as Nepenthes, Utricularia, etc.

Most significant function of

leaves is photosynthesis.

Veins of the leaves help

in conduction of inorganic

and organic nutrients.

Gaseous exchange from

and to the atmosphere

takes place through

stomata present in leaves.

Primary functions Secondary functions

Prophylls

The first few leaves on a stem

which differ from other leaves.

Fig.: Prophylls

Bracteoles

Two small leaf like structures directly subtending a flower

found whose stalk itself is subtended by a bract, e.g.,

Adhatoda.

Cotyledonary

Embryonic leaves emerging at the time

of seed germination, e.g., dicot and

monocot.

Cotyledonary leaves

Fig.: Cotyledonary

leaves of Ricinus

Bract leaves

Leaves containing flower or inflorescence

in their axil, e.g., Bougainvillea.

Bract leaves

Fig.: Bract leaves of

Bougainvillea

Cataphylls

Small, sessile, non-chlorophyllous,

membranous structures occurring on

underground stems, e.g., Zingiber

officinale and aerial stem, e.g., Ruscus.

Scaly leaves

Fig.: Scale leaves

of ginger

Sporophylls

These are also called as floral leaves,

e.g., sepals, petals, androecium and

gynoecium. These are modified

leaves.

Floral leaves

Fig.: Floral leaves

of a flower

Other Types of Leaf(On the basis of origin and functions, leaves can be):

Thorns, Spines, Prickles and Bristles

Thorns are sharp, pointed, straight or curved hard structures that prevent excessive transpiration and protect plant from grazing animals.

Spines are modified leaves or parts of leaf (a vascular strand without well developed bark).

Prickles refers to superficial outgrowths of stem or leaves that do not possess a vascular cylinder and hence can easily be separated.

Bristles are stiff hair like structures that become thickened due to deposition of silica or calcium carbonate.

INFLORESCENCE

• The arrangement and distribution of flowers on the shoot system of a plant is called inflorescence.


• It refers to the modified shoot specialised to form flowers.


• The axis of the inflorescence is called peduncle. The stalk of the individual flower is called pedicel.


• Five main types of inflorescence are recognised. These are solitary, racemose, cymose, mixed and specialised.

Flowers occur singly

or are separated from

other flowers of the

same plant by means

of vegetative regions.

Solitary

Solitary terminal

Single flower occurs

on the terminal

part of a main stem

and its branches,

e.g., poppy.

Flower

Leaf

Pedicel

Fig.: Solitary terminal

flower of poppy

Solitary

axillary

Single flower

occurs in the

axil of a leaf,

e.g., Petunia,

China rose. Fig.: Solitary axillary

inflorescence of Hibiscus

Flower

Stem

Pedicel

Leaf