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PinkMonkey Online Study Guide-Biology

4. Lichens and mycorrhiza

Lichens

It is an obligatory association between an alga and a fungus, which together form a closely integrated unit.

The body of a lichen is composed of branching hyphae of a fungus, which harbor algal cells. The fungus gets food synthesized by the alga and the alga in return gets shelter, moisture and minerals absorbed by the fugal partner from the substrate.

Lichens are classified into three principle groups as follows:

Figure 14.49 Types of lichens

(1) Crustose lichens : These lichens form a hard granular crust closely adhering to rocks and tree trunks, e.g. Graphics.

(2) Foliose lichens : These lichens form leaf-like thalli with lobed margins attached to tree trunks, rocks, walls, etc. They are sometimes referred to as shelf fungus.
e.g. Parmelia.

(3) Fruticose lichens : These lichens form much branched shrub-like habit developing fruiting bodies, e.g. Usnea.


Economic importance of lichens : Lichens are used in varieties of ways. Some lichens are valuable source of food to wild animals like reindeer. Some lichens are fried and given to cattle as food and to some extent to human beings. Some are used in medicines and other are for preparation of dyes. Litmus is prepared from certain lichens and some are also used in the preparations of cosmetics and perfumes.

Ecological significance : Lichens growing on rocks disintegrate them to form soil, preparing the ground for mosses and subsequently for higher plants. Thus, they help in the succession of plant communities.

Mycorrhiza

Symbiotic and usually non-pathogenic associations of fungi with roots of higher plants, are called mycorrhiza. They are observed in 90% of higher plants.

Figure 14.50 Mycorrhiza in Pinus root

The fungus decomposes the organic material in the soil, thus making minerals available to plants, while in return they get sugars, amino acids and other organic substances from the plant. It has been observed that many forest plants die due to malnutrition when the soil lacks appropriate fungi. The best known mycorrhizas are those of forest trees like Pinus and orchids.

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Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi

Chapter 15





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