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CHAPTER 5 : FUNGIHALIMAHTUN SAEDIAH BT ABU BAKAR

KOLEJ TEKNOLOGI TIMUR, SEPANG

Introduction

• The Kingdom Fungi includes some of the most important organisms, both in terms of their ecological and economic roles.

• By breaking down dead organic material, they continue the cycle of nutrients through ecosystems.

• Fungi are frequently found among the microbiota of soil and aquatic ecosystems.

• A major role of these fungi is as decomposers where they decompose dead and decaying organic matter.

• Some species of fungi have adapted to a parasitic life style, causing disease in animals and plants.

Introduction

• Fungi are important both as a source of food and in the preparation of food.

• Edible fungi include mushrooms, truffles, and morels.

• Bread, beer and wine are produced through the action of fungi known as yeasts, such as Saccharomyces cerevisae.

• Other fungi provide numerous drugs such as penicillin and other antibiotics.

Introduction• Fungi also are important crop parasites, causing loss of food

plants, spoilage of food and some infectious diseases.• Like plants and animals, fungi are eukaryotic multicellular

organisms. • Another feature of fungi is the presence of carbohydrate

chitin in their cell walls. • This is a long carbohydrate polymer that also occurs in the

exoskeletons of insects, spiders, and other arthropods. • The chitin adds rigidity and structural support to the thin

cells of the fungus, and makes fresh mushrooms crisp.

Nutrition and Lifestyles of Fungi

• All fungi are heterotrophic, meaning that they obtain their energy and carbon compounds from the metabolism of organic nutrients.

• None of the fungi are photosynthetic. • Species of fungi are divided into the following

three categories:a) Mycorrhizal fungi form a partnership with most

vascular plants. b) Parasitic fungi prefer the living host; this category is

fairly small.c) Saprophytic fungi prefer dead and decaying material

MYCORRHIZAL• Mycorrhizal fungi form a partnership mainly with vascular

plants, rather then harming the tree, their presence significantly increases the roots' effectiveness.

• Fungi send their hyphae in and about the little rootlets of the tree until it’s difficult to tell them apart.

• The tree supplies the mycelium with moisture and carbohydrates, and the mycelium returns the favour with minerals and other nutrients from the surrounding soil.

• Mycorrhiza fungi are beneficial both in nature and agriculture; plants with them tend to grow better than those without.

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PARASITIC

• Parasitic fungi are the second largest group, of whose members do a lot of serious damage.

• Rather than obtaining their food from dead animals or plants, they prefer a living host, often attacking and killing, it then living on as a saprophytic fungi.

Mutualistic and parasitic fungi develop specialized hyphae known as haustoria that able to enter the cell walls of plants.

SAPROPHYTIC• Saprophytic fungi are the largest group of fungi, they growing on

dead organic matter such as fallen trees, cow patties, dead leaves, and even dead insects and animals.

• They are absorptive heterotrophs They secrete powerful hydrolytic enzyme known as exoenzymes that work to "rot" or "digest" the breakdown their complex food.

• Exoenzymes break down complex molecules into smaller organic compounds.

• The fungi then absorb the resulting small organic compounds through their cell wall.

• Fungal hyphae have a small volume but large surface area, enhancing the fungal absorptive capacity.

• Without their digestive activities, organic material would continue to accumulate until the forest became a huge rubbish dump of dead leaves and trees.

Body Structure

• Single-celled fungi are called yeasts. Yeasts generally reproduce by a type of cell division called budding, in which a small cell, or bud, forms on the parent cell and grows until it splits off.

• Fungi are single-celled or multicellular. The cells of multicellular fungi are arranged in long filaments of end-to-end cells called hyphae (singular: hypha).

• Actually, the term “multinuclear” might be more appropriate than “multicellular” because, in many cases, there is no actual separation between the nuclei in the hyphae.

• Fungal hyphae can be divided into two main groups, based on the amount of separation that exists between their nuclei: – Nonseptate hyphae or coenocytial hyphae: In

nonseptate hyphae, the nuclei inside the filament are not separated by cell walls. As the hypha grows and gets longer, the nuclei reproduce by mitosis, but there is no cytokinesis or cell wall formation between the new nuclei.

– Septate hyphae: In this type of hyphae, the nuclei are separated by cell walls. When a nucleus divides by mitosis, a cell wall partition or septum forms between the new nuclei. Even in septate hyphae, however, the separation is not complete; there are pores in the septa that allow movement of cytoplasm between the cells.

Structure of hyphae

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• Fungal hyphae are found in randomly tangled masses called mycelia (singular: mycelium).

• In molds, the mycelia often spread to fill the available space, limited by available nutrients.

• The fleshy fungi have mycelia that are structured into well-defined forms or morphologies, such as in mushrooms.

• Even in mushrooms, there is very little tissue-level differentiation.

• Hyphae that have two genetically distinct, sexually compatible nuclei within each cell are dikaryotic, where it is described as n+n, not 2n because there are two separate haploid nuclei.

• Hyphae that have only one nucleus per cell are described as monokaryotic.

• Some fungi can exist as either yeasts or hyphae, depending on the environmental growth conditions.

• These are called dimorphic fungi. Several important pathogenic species are dimorphic.

Reproduction in Fungi• Sexual reproduction in fungi starts when hyphae from

different mycelia release sexual signaling molecules called pheromones.

• When the hyphae meet, they fuse. The union of the cytoplasm of two parent mycelia is known as plasmogamy.

• In several fungi, the haploid nuclei contributed by each parent do not fuse immediately.

• Instead, parts of the mycelia contain coexisting, genetically different nuclei.

• Such mycelium is said to be heterokaryon or ‘different nuclei’.

Reproduction in Fungi

• In some fungi, the haploid nuclei pair off to a cell, one from each parent.

• Such mycelium is said to be dikaryotic or ‘two nuclei’.

• As a dikaryotic mycelium grows, the two nuclei in each cell divide as a pair without fusing.

• The next stage in the sexual cycle is karyogamy. • Karyogamy occurs hours, days or even centuries

after the occurrence of plasmogamy.

Reproduction in Fungi

• During karyogamy, the haploid nuclei from the two parent fuse, producing diploid cells.

• Zygotes and other short-lived structure form during karyogamy.

• Meiosis brings back the haploid condition, and next mycelium makes specialized reproductive structures that produce and disperse the haploid spores.

• The sexual processes of karyogamy and meiosis result in genetic variation.

Asexual Reproduction in Fungi

• Besides sexual reproduction, many fungi can reproduce asexually.

• Clones are generated by mitotic production of spores that can be dispersed by air or water. Several fungi which can reproduce asexually grow as mold.

• Molds grow as mycelia and produce spores. • Many species of molds can also reproduce

sexually if they came in contact with other mating types.

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Asexual Reproduction in Fungi

• Other type of asexual fungi is yeast. • Instead of producing spores, yeast reproduces

asexually by simple cell division or by budding. • Sometimes yeast can also reproduce sexually.• A lot of mold and yeasts have no known sexual

stage. • These fungi are called deuteromycetes or

imperfect fungi. • It is referred to imperfect fungi due to sexual

stages of life cycles.

Generalized life cycle of fungi

Classification of Fungi

• Over 60,000 species of fungi are known. • Fungi are classified based mainly on the

characteristics of their sexual spores and fruiting bodies.

• However, molecular data such as comparative DNA and RNA sequences is getting important in determining relationships among fungi.

Classification of Fungi

• It seems likely that fungi are not a monophyletic group. They have been divided into five taxonomic divisions: 1. Chytridiomycota2. Zygomycota3. Ascomycota4. Basidiomycota

Classification of fungi

CHYTRIDIOMYCETES

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Chytridiomycetes

• Chytridiomycetes are members of phylum Chytridiomycota.

• The chytrids, represents a group of primitive aquatic fungi.

• Chytridiomycetes are parasites or decomposers that inhabit mainly fresh water, although some species inhabit moist soil and in marine water.

Chytridiomycetes

• Chytridiomycetes have cell wall containing chitin and store their food reserves as glycogen.

• They are characterized by having gametes that are motile by means of flagella.

• They can reproduce sexually and asexually.

Chytridiomycetes

• Allomyces is one common example of chytridiomycetes.

• It has alternation of generations in its life cycle, where it spend part of its life as haploid (n) thallus and the other part as a diploid (2n) thallus.

• The haploid and diploid thalli look the same in apperarance that consist of a stout stalk like part with slender branches.

Chytridiomycetes

• The haploid thallus produces male and female gametangia.

• Gametangia are the structures where gametes are formed through mitosis and they are located at the tip of the branches.

Chytridiomycetes

• The haploid flagellated gametes are release from the gametangia.

• Fusion of haploid flagellated male gamete with haploid flagellated female gamete form diploid zygote, which develop into a diploid thallus.

• The diploid thallus produces resting sporangiaand zoosporangia.

Chytridiomycetes

• Zoosporangia produce flagellated diploid zoospores that may land on substrate and grow into new diploid thalli.

• Meanwhile, meiosis occurs in the resting sporangia to form haploid zoospores.

• When each of the haploid zoospores land on suitable substrate, it will germinate and develop into a haploid thallus.

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ZYGOMYCETES

Zygomycetes

• The zygomycetes are members of phylum or division Zygomycota.

• The division Zygomycotaconsists of fewer than 1000 species.

• They are characterized by the formation of sexual spores called zygospores.

• Most zygomycetes are decomposers, which live in the soil on decomposing plant and animal matter.

• Some are parasites of plants and animals and others form mycorrhiza with plant roots.

Zygomycetes

• An example of a zygomycete is the common black bread mold, Rhizopus stolonifer, a decomposer that decomposes bread and other foods.

• When a spore falls on bread, it will germinates and grows into mycelium.

• Horizontal hyphae spread, penetrate the food or bread and absorb nutrients.

Zygomycetes

• The hyphae are coenocytic, with septa found only where reproductive cell are formed.

• Finally, certain hyphae grow upward and form spore sacs known as sporangia at their tips.

• Within each stalked sporangium, clusters of asexual black spore develop and are dispersed when the fragile sporangium bursts.

• If the spores land on moist food, it germinates and grows into new mycelia.

Zygomycetes

• If environment become unfavorable, such as the mold does not have enough supply of food, Rhizopus will perform sexual reproduction.

• Sexual reproduction occur when the hyphae of two different mating types, shown designated as (+) and (–) become in contact with one another.

• The bread mold is heterothallic, where the fungal hypha can only mate with a hypha of different mating type, such as (+) and (-), not between (+) and (+) or (-) and (-).

Zygomycetes

• When hyphae of different mating types grow very close to one another, hormones are produced and this causes the tips of hyphae to come together and develop gametangia on each tip.

• The gametangia fuse, followed by the nuclei to form zygote with diploid nucleus.

• The zygote develops into a zygospore, enclosed by thick-walled covering known as zoosporangium.

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Formation of zygospores

• The zygospore may lie dormant until the condition become favorable.

• Meiosis occurs before germination of zygospore. When the haploid zygosopore germinates, aerial hyphae formed with a sporangium at the tip.

• Mitosis occurs in the sporangium to produce haploid spores.

• The genetically diverse haploid spores are released from the sporangium and when germinate will develop into new hyphae.

Life cycle of Rhizopus

stolonifer, black bread

mold

ASCOMYCETES

Ascomycetes

• The ascomycetes are members of the phylum or division Ascomycota.

• The division Ascomycota contains more than 30,000 species of unicellular yeasts to multicellular fungi.

• They are also called the “sac fungi” because their sexual spores (ascospores) are enclosed in tube-like sacs known as asci. (sing. ascus).

Ascomycetes

• The formation of ascospores is similar to that of zygospores, except that the ascosporesformed by meiosis are enclosed in the asci.

• Unlike zygomycetes, most ascomycetes bear their sexual stages or asci in fruting bodies known as ascocarps.

• Ascocarp can range in size from microscopic to macroscopic in size.

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Ascomycetes

• Most ascomycetes reproduce asexually by producing spores called conidia.

• Conidia are formed externally at the tips of specialized hyphae known as conidiophores, often in cluster or long chain where they can be dispersed by the wind and germinate when land on the suitable substrate and the condition is favorable.

• Conidia can be found in various shapes, sizes, and colors in different species.

• Some species of ascomycetes have different mating strains and known as heterothallic and others are homothallic, where they are self-fertile and able to mate with themselves.

• Neurospora crassa is an ascomycete mold that is heterothallic or has different mating types.

• In both heterothallic and homothallic ascomycetes, sexual reproduction occurs when two gametangia become in contact with one another and then fuse.

• Within this fused structure, the plasmogamyor mixing of cytoplasm occurs but the haploid nuclei from each parent hypha do not fuse.

• New hyphae where the cells of which are dikaryotic, grow from the fused structure and branch repeatedly until the tips of these dikaryotic hyphae develop into dikaryotic asci.

• As the many dikaryotic asci develop, they are enclosed by intertwining hyphae that develop into a fruiting body known as ascocarp.

• Within an ascus, karyogamy unites the two nuclei to form diploid nucleus, the zygote.

• This zygote then undergoes meiosis to forms four genetically different haploid nuclei.

• Each of the haploid nuclei undergoes mitotic division to form eight heavy-walled ascospores.

• Thus there are eight ascospores line-up within each ascus.

• The ascospores are finally released from the ascocarp and if one lands on suitable substrate and condition is favorable, it germinates and forms a new mycelium.

• Phylum ascomycota consist of more than 300 species of unicellular yeasts.

• Yeasts reproduce asexually by budding and binary fission.

• In binary fission, they undergo mitosis and then divide into half.

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• Some yeasts reproduce sexually by forming ascospores in a sac or ascus.

• In sexual reproduction, two haploid yeasts fuse to form a diploid zygote.

• The zygotes undergo meiosis to form haploid nuclei that developed into ascospores.

• These ascospores are enclosed within their original cell wall that acts like an ascus. One example of yeast is Saccharomyces cerevisiae.

The reproductive

cycle of an ascomycete

BASIDIOMYCETES

Basidiomycetes

• Basidiomycetes, also known as the “club fungi,” are classified in phylum or division Basidiomycota. Basidiomycetes include some of the most complex fungi, including mushrooms, bracket fungi and puffballs.

• Their sexual spores, or basidiospores, are formed on complex fruiting body structures called basidia(sing. basidium). Basidium is an enlarged hyphalcell and at the tip of this basidium developed four basidiospores.

Basidiomycetes

• Each of the basidiospores is able to germinate and form new primary haploid mycelium. Hyphae of a haploid primary mycelium consist of monokaryotic cells. The hyphae are divided into cells by perforated septa that allow cytoplasmic streaming between cells.

Basidiomycetes

• When two haploid primary mycelia of different mating types encounter with one another, the hypha of the mycelia fuse and undergo plasmogamy. A dikaryotic secondary mycelium develops, grows faster than the parental mycelia and finally become crowded.

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Basidiomycetes

• When the environmental condition is favorable, the secondary mycelia form compact mass, called buttons, along them.

• Each button grows into fruiting body known as basidiocarps or mushroom.

• Each basidiocarp or mushroom consists of a stalk and a cap.

Basidiomycetes

• The lower surface of the cap normally consists of numerous vertical thin plates known as gillsthat radiate from the stalk to the edge of the cap.

• The basidiocarp gills are lined with terminal dikaryotic cells called basidia.

Basidiomycetes

• The haploid nuclei in the basidia then undergo karyogamy to form diploid nuclei, the zygote, which then undergoes meiosis.

• Each diploid nucleus produces four haploid nuclei.

Basidiomycetes

• Each basidium grows four extensions, where one haploid nucleus and some cytoplasm get into each extension.

• Each of these extensions then develops into a basidiospore.

• When the basidiospores mature, they will be released from the basidium, fall from the cap, and distributed by the wind.

• When the condition is favorable, the basidiospores germinate and develop into short-lived haploid primary mycelia.

Fruiting structure of a mushroom.

THE LIFE CYCLE OF TYPICAL

BASIDIOMYCETE

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IMPORTANCE OF FUNGI

Fungi and environment

• Many saprotrophs fungi act as decomposer and break down organic compound, absorbing nutrient from organic waste and dead organisms. They help in the cycling of nutrient in our ecosystem.

• Some of them performs mutualistic relationship with other organisms such as mycorrihizae. Mycorrhizae are mutualistic relationships between fungi and the roots of plants.

Fungi as pathogens

• Some are parasites that live in other organisms and causing harmful effects such as diseases to their host organisms.

• Some fungi are pathogenic that causes animal diseases that infects on skin, hair, nail and even internal tissues and organs.

Fungi as pathogens

• Human diseases such as ringworm, athlete’s foot, candidiasis and histoplasmosis are caused by fungi.

• Candida causes yeast infections of mucosal membranes.

• Serious systemic infections such as histoplasmosis, form spores in bird feces.

• Aspergilus fumigatus usually not a problem but become a serious pathogen in people with AIDS.

Fungi as pathogens

• Fungi can cause mycotoxins; some are dangerous. • Aflatoxin form in peanuts, pecans, corn, and

other grains, is one of the most potent carcinogens and toxins known; are made by fungi.

• Some fungi can cause diseases in plants. • Some ascomycetes are parasites responsible for

wheat, rust Dutch Elm disease and Chestnut blight.

• Amanita phalloides is the most poisionous of all mushrooms.

Fungi in industry

• Mushrooms, morels and truffles are used as foods.

• Club fungi are important as commercial crops. • Agaricus campestris is the common mushroom

found in grocery stores. • Other sac fungi such as yeasts are used in

commercial baking of bread, production of alcoholic beverages.

• Fungi such as ascomycete Penicillium are used to produce cheeses and Aspergillus tamarii produce soy sauce by fermenting soya beans.

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Fungi in industry

• Fungi are used in producing chemical compopunds that are important in food-processing industry such as citric acid and gluconic acid.

• Fungi are also used in the production of penicillin and other antibiotics.

• Penicillin produces by Penicillium notatum. • Many drugs such as griseofulvin (fungal inhibitor),

lovastatin (cholesterol drug) and cyclosporine (immune system suppressor used for cancer treatments are fungal-derived.

Fungi in industry

• Ergot produced by ascomycete Claviceps papureais used to produce certain drugs. Clavicepspapurea infects flowers of rye plants and other cereals.

• Derivatives of ergot-induced drugs used for labor induction, to stop uterine bleeding, to treat high blood pressure, and to relieve migraine headache.

• Other fungi make citric acid and many other industrial chemicals.

Fungi in industry

• Other mushrooms have hallucinogenic properties such as the drug psilocybin important in native religious rituals in Central and South America.

• Yeasts are part of the Human Genome Project and serve as easily studied models for eukaryotic gene systems.

• Yeast chromosomes have also been modified to serve as vectors for transporting human DNA fragments for use in gene mapping.

LICHENS

Lichens• Lichens are symbiotic organisms made up by the

association of microscopic green algae or cyanobacteria and filamentous fungi.

• Symbiotic relationship means that it is two or more organisms living together such that both are more successful within the partnership than they would have been if they were living on their own.

• The fungi is known as 'mycobiont' and one or more algae and/or a cyanobacteria are called the 'photobiont'.

Lichens

• The fungal partner benefits by getting sugars, its only nutriment from the algae which being green synthesizes sugars through photosynthesis.

• The algal partner gets protection as the fungi normally forms the outer surface.

• This protection is against the weather mostly, it results in the algae having a more stable and constant environment to live in allowing it to grow better.

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Lichens

• The fungi collect the sugars by means of special hyphae called haustoria which penetrate the wall of the algal cells.

• The fungi may produce a substance which increases the permeability of the algal cell walls such that the cells lose as much as 80% of the sugars that they produce.

• The sugars pass into the fungal hyphaethrough diffusion.

Lichens

• Lichens take the external shape of the fungal partner and hence are named based on the fungus.

• The fungus most commonly forms the majority of the lichen's bulk.

• The lichen fungus is typically a member of the Ascomycotaand rarely a member of the Basidiomycota.

• Some lichen taxonomists place lichens in their own division, the Mycophycophyta

• Lichens reproduce mostly by asexual methods, normally by fragmentation.

• It is a process in which special dispersal units of the lichen, known as soredia.

• Soredia are small bundles of algal cells in a fungal hyphae mesh.

• When the soredia break off, and if they land on a suitable substrate, they will germinate to form new lichens.

• Morphologically, lichens are made up of a few distinct characters.

• The most obvious is the thallus. • The form of the thallus is a result of the fungal

species involved. • The thallus is the body of the lichen.

• The fungal hyphae or filaments branch and then fuse together when they meet to form a mesh of hair-like threads.

• The top surface is normally a layer of tightly packed hyphae called a 'cortex'.

• Below this is the algal layer where the photobiontlives.

• Below this is the medulla, an area of loose hyphae in which nutrients are stored.

• Sometimes a lower cortex exists, in others the medulla rests on the surface.

Generalized structure of a lichens

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Lichens occur in one of four basic growth forms, as illustrated below:

1. Crustose - crustlike, growing tight against the substrate.

2. Squamulose - tightly clustered and slightly flattened pebble-like units.

3. Foliose - leaflike, with flat sheets of tissue not tightly bound.

4. Fruticose - free-standing branching tubes.

Various forms of lichens

Crustose lichens• Crustose lichens form a crust on the surface of the

substrate on which they are growing. • This crust can be quite thick and granular or actually

embedded within the substrate. • In many crustose lichens the surface of the thallus

breaks up into a cellular, crazy-paving like pattern. • Crustose lichens tend to grow out from their edges and

have their fruiting bodies in their centre. • Crustose lichens are very difficult to remove from their

substrates. • In crustose lichens there is no lower cortex.

Squamulose lichens

• Some lichens have a portion of their thalluslifted off the substrate to form 'squamules'.

• They are otherwise similar to crustose lichens in that they possess an upper cortex but no lower cortex.

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Foliose lichens

• These have an upper and lower cortex. • They are generally raised to some extent

above the substrate but connected to it by specialised root-like hyphae known as rhizines.

• They are easier to remove from their substrate when collecting because of this.

Fruticose lichens

• Fruticose lichens are shrubby lichens. • They are attached to their substrate by a

single point and rise, or more usually, hang down from this.

• In fruticose lichens, the algal part exists as a ring around the thallus, even when it is flattened.

• In fruticose lichens the lower cortex is replaced by a central one.

Old Man's Beard, Usnea

spp. is a common

green-grey lichen seen

hanging from trees.

IMPORTANCE OF LICHENS

• Lichens are amongst the slowest-growing organisms, but their tolerance of environmental extremes enables them to colonize habitats where few other macroscopic organisms can grow.

• They grow where neither the fungal partner nor the photosynthetic partner could survive alone, because they benefit from their unique symbiotic association.

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IMPORTANCE OF LICHENS

• Lichens play important roles in ecosystems. • They break down rocks and form soil by

excreting weak acids, or in arid ecosystems like deserts, they help bind the soil surface by forming crusts.

IMPORTANCE OF LICHENS

• They are important food sources for invertebrates and vertebrates, including reindeer in tundra that eat reindeer "moss," which is actually a lichen.

• In addition, some birds depend on certain lichens for nest-building materials.

• Finally, some lichens can fix nitrogen from the atmosphere and contribute a significant portion of this to certain forest ecosystems.

IMPORTANCE OF LICHENS

• Although lichens typically grow in harsh environments in nature, many lichens are sensitive to man-made pollutants.

• Hence, they have potential as pollution indicator organisms.

IMPORTANCE OF LICHENS

• Moistened lichen tissues act as blotters, soaking up chemicals or materials deposited on their surfaces.

• Unfortunately, this feature has also made them highly susceptible to air pollutants; lichens are perhaps the plant species most susceptible to sulfur dioxide, heavy metals, and acid rain.

THE END