LEAF

Leaves are green, thin flattened lateral outgrowths of the stem. They are borne at the nodes of the stem. Leaves are the chief organs of photosynthesis. The green leaves of the plant are collectively called as foliage of the plant.

Parts of a Leaf The three main parts of a typical leaf are

1. Leaf base

2. Petiole

3. Lamina

Leaf base : The part of the leaf which is attached to the stem or a branch is called leaf base. In some plants the leaf has a swollen leaf base. It is known as pulvinus eg. The compound leaves of the family Fabaceae.

In monocots the leaf base is very broad and flat and it clasps a part of the node of the stem as in maize and in banana. It is called sheathing leaf base.

Stipules: In most of the dicotyledonous plants, the leaf-base bears two lateral appendages called the stipules. Leaves which have the stipules are called stipulate.

The leaves without stipules are called exstipulate. The main function of the stipule is to protect the leaf in the bud.

Petiole : Petiole connects the lamina with the stem or the branch. A leaf is said to be petiolate when it has a petiole. It is said to be sessile when the leaf does not have a petiole.

Leaf blade: It is also known as lamina. This is the most important, green part of the leaf which is mainly concerned with the manufacture of food. The lamina is traversed by the midrib from which arise numerous lateral veins and thin veinlets.

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CONCEPT OF FLOWER

The concept that the flower is a modified or a metamorphosed shoot for the purpose of reproduction is an old one and the concept is gradually developed through the past and is accepted at the present by a majority of morphologists.

Linnaeus expressed this idea in his Philosophia Botanica (1751) by the phrase “vegetative metamorphosis”.

This concept that floral leaves were a modification of vegetative leaves was further elaborated by Caspar Wolff and Decandolle.

The ‘ foliar theory’ of the flower of the earlier botanists is held today by many though modified in one form or other by other botanists. That the flower is a modified shoot, is only a figurative expression, and implies that the floral leaves are vegetative leaves and transformed to do a different function of reproduction, in the place of the ordinary function of photosynthesis.

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