Question

modification of leaves​

Answer 1

In many plants, leaves get modified to perform some special functions other than the normal ones, such as photosynthesis and transpiration.

Sometimes these modifications are in response to certain environmental conditions.

Some of the important modifications are given below:

1. Storage Leaves:

Some plants of xerophytic habitats and members of the family Crassulaceae generally have highly thickened and succulent leaves with water storage tissue. These leaves have large parenchymatous cells with big central vacuole filled with hydrophilic colloid. This kind of adaptation helps plants to conserve very limited supply of water and resist desiccation (drying up).

2. Leaf Tendrils:

In weak- stemmed plants, leaf or a part of leaf gets modified into green thread­like structures called tendrils which help in climbing around the support.

4. Scale-leaves:

Typically these are thin, dry, stalkless, membranous structures, usually brownish in colour or sometimes colourless. Their function is to protect the axillary bud that they bear in their axil. Sometimes scale-leaves are thick and fleshy, as in/onion; then their function is to store up water and food. Scale-leaves are common in parasites, saprophytes, underground stems, etc. They are also found in Casuarina, Asparagus etc.

5.. Leaflet Hooks:

In Bignonia unguiscati the three terminal leaflets of leaf get modified into claw like hooks which help in climbing (Fig. 4.29).

6. Leaf Roots:

In case of Salvinia three leaves are present at one node. Out of these two leaves are normal and third gets modified into adventitious roots which help in floating over the surface of water

7. Phyllode:

In Australian Acacia (Fig. 4.31) the petiole or any part of the rachis becomes flattened or winged taking the shape of the leaf and turning green in colour. This flattened or winged petiole or rachis is known as the phyllode. The normal leaf which is pinnately compound in nature develops in the seedling stage, but it soon falls off. The phyllode then performs the functions of the leaf. In some species, however, young or even adult plants are seen to bear the normal compound leaves together with the phyllodes.

There are about 300 species of Australian Acacia (Acacia moniliformis), all showing the phyllodes. In lerusalem thorn (Parkinsonia; fig. 4.32), a small prickly tree, the primary rachis of the bipinnate leaf ends in a sharp spine, while each secondary rachis is a phyllode being green and flattened. The leaflets are small and fall off soon. The phyllode then performs the functions of the leaflets.

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