| Fungi |
Above: a bracket fungus. These fungi are usually found on the sides of trees and on fallen logs. This
one is probably growing on a decomposing log beneath the soil surface. Fungi were once classed as
plants, but they do not photosynthesise, but instead obtain nourishment from preformed organic
materials, in much the same way that animals do. Many are saprotrophic - feeding off decomposing
organic remains, such as dead wood. Some are parasitic and may feed off the living tissues of plants
(and sometimes animals). Others exist in harmonious symbiosis with organisms that can
photosynthesise. Most trees require such fungal symbionts if they are to grow properly (especially on
poorer soils). These fungi associate with plant roots, forming mycorhizae (or mycorhizas, lit. 'fungus
roots', sing. mycorhiza). The body of a fungus is an often large and diffuse mass of whitish hairlike
threads that spread through soil, rotting logs or living wood in the case of parasites. This mass is called
the mycelium. The part of the fungus that is usually visible are the sporocarps or sporing bodies, like
those shown above. Periodically the mycelium puts out these structures into the open to shed spores.
The mycelium is made up of fine hairlike fibres called hyphae. Hyphae have a very large surface area
to volume ratio, which makes them exceptionally good at absorbing nutrients. The hyphae secrete
enzymes (or rely on those secreted by other micro-organisms) into their food, digesting it and then
absorbing the nutrients with their hyphae. In the case of mycelia, the hyphae are especially good at
absorbing hard-to-get soil nutrients like phosphorus, indeed they are much better than plant roots at
this. They give the plant roots some of these minerals in exchange for sugars manufactured by the
plant during photosynthesis.
The diagram below shows the mycorhiza of the beech tree (Fagus sylvatica). The mycelium forms a
hairlike net that en-sheaths part of the root, this is called the Hartig net. Some of these hyphae
penetrate between the root epidermal cells, which form the outer layer of root tissue.
one is probably growing on a decomposing log beneath the soil surface. Fungi were once classed as
plants, but they do not photosynthesise, but instead obtain nourishment from preformed organic
materials, in much the same way that animals do. Many are saprotrophic - feeding off decomposing
organic remains, such as dead wood. Some are parasitic and may feed off the living tissues of plants
(and sometimes animals). Others exist in harmonious symbiosis with organisms that can
photosynthesise. Most trees require such fungal symbionts if they are to grow properly (especially on
poorer soils). These fungi associate with plant roots, forming mycorhizae (or mycorhizas, lit. 'fungus
roots', sing. mycorhiza). The body of a fungus is an often large and diffuse mass of whitish hairlike
threads that spread through soil, rotting logs or living wood in the case of parasites. This mass is called
the mycelium. The part of the fungus that is usually visible are the sporocarps or sporing bodies, like
those shown above. Periodically the mycelium puts out these structures into the open to shed spores.
The mycelium is made up of fine hairlike fibres called hyphae. Hyphae have a very large surface area
to volume ratio, which makes them exceptionally good at absorbing nutrients. The hyphae secrete
enzymes (or rely on those secreted by other micro-organisms) into their food, digesting it and then
absorbing the nutrients with their hyphae. In the case of mycelia, the hyphae are especially good at
absorbing hard-to-get soil nutrients like phosphorus, indeed they are much better than plant roots at
this. They give the plant roots some of these minerals in exchange for sugars manufactured by the
plant during photosynthesis.
The diagram below shows the mycorhiza of the beech tree (Fagus sylvatica). The mycelium forms a
hairlike net that en-sheaths part of the root, this is called the Hartig net. Some of these hyphae
penetrate between the root epidermal cells, which form the outer layer of root tissue.
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A single fungus may, in this way, connect the roots of several trees together. The roots of neighbouring
trees may also naturally graft directly together, especially if the trees belong to the same species. Such
grafted roots can exchange nutrients and this helps the weaker trees. If a tree is felled, the stump may
regenerate (depending on the species) by putting out new shoots. Some of the nutrients for this growth may
come from neighbouring trees through the interconnected root network.
Some fungi can form mycorhizas with a variety of different trees, but each woodland type, such as beech,
birch, oak or pine, has its own characteristic set of mycorhizal fungi. For example, the fly agaric, Amanita
muscaria, will only grow under birch and pine. Likewise, each species of tree is often capable of forming
mycorhizas with several different fungus species. These fungi may or may not contribute to leaf litter
decomposition, but they are good at extracting nutrients like phosphate. Brushing aside the leaf-litter in a
beechwood will reveal the tiny feeder roots that protrude vertically into the leaf-litter and these coral-like
roots are the mycorhizas.
Orchids characteristically form mycorhizas of a type called endomycorhizas - in this type there is no external
hyphal sheath, or Hartig net, around the root, and the fungal hyphae penetrate and internally invade the
cells in the outer layers of the root. Deeper in the root is a zone in which cells are digesting the fungal
hyphae and the central zone is fungus-free. These fungi can digest cellulose and lignin (present in plant
remains) and the relationship appears a complex and unsettled one. The orchids need the mycorhizas
when they are young germlings and seedlings. The seeds will not germinate without their fungal partner,
however, sometimes the fungus infects and consumes the seed, destroying it. This illustrates how these
mutualistic symbioses cover a spectrum of relationships, with the fungus parasitising the plant on one hand,
and the plant eating the fungus on the other. Some orchids are non-photosynthetic and lack green
chlorophyll and these depend on their fungal partner to provide them food throughout their life. In contrast
to the mycorhizas of trees, in which the fungus provides minerals and the plant sugars, in orchid mycorhizas
the fungus appears to be supplying the plant with sugars by digesting cellulose. In this way many orchids
are able to feed saprotrophically as well as photosynthetically. Many other herbaceous plants rely on
mycorhizas, but mycorhizas tend to be absent from grassland.
trees may also naturally graft directly together, especially if the trees belong to the same species. Such
grafted roots can exchange nutrients and this helps the weaker trees. If a tree is felled, the stump may
regenerate (depending on the species) by putting out new shoots. Some of the nutrients for this growth may
come from neighbouring trees through the interconnected root network.
Some fungi can form mycorhizas with a variety of different trees, but each woodland type, such as beech,
birch, oak or pine, has its own characteristic set of mycorhizal fungi. For example, the fly agaric, Amanita
muscaria, will only grow under birch and pine. Likewise, each species of tree is often capable of forming
mycorhizas with several different fungus species. These fungi may or may not contribute to leaf litter
decomposition, but they are good at extracting nutrients like phosphate. Brushing aside the leaf-litter in a
beechwood will reveal the tiny feeder roots that protrude vertically into the leaf-litter and these coral-like
roots are the mycorhizas.
Orchids characteristically form mycorhizas of a type called endomycorhizas - in this type there is no external
hyphal sheath, or Hartig net, around the root, and the fungal hyphae penetrate and internally invade the
cells in the outer layers of the root. Deeper in the root is a zone in which cells are digesting the fungal
hyphae and the central zone is fungus-free. These fungi can digest cellulose and lignin (present in plant
remains) and the relationship appears a complex and unsettled one. The orchids need the mycorhizas
when they are young germlings and seedlings. The seeds will not germinate without their fungal partner,
however, sometimes the fungus infects and consumes the seed, destroying it. This illustrates how these
mutualistic symbioses cover a spectrum of relationships, with the fungus parasitising the plant on one hand,
and the plant eating the fungus on the other. Some orchids are non-photosynthetic and lack green
chlorophyll and these depend on their fungal partner to provide them food throughout their life. In contrast
to the mycorhizas of trees, in which the fungus provides minerals and the plant sugars, in orchid mycorhizas
the fungus appears to be supplying the plant with sugars by digesting cellulose. In this way many orchids
are able to feed saprotrophically as well as photosynthetically. Many other herbaceous plants rely on
mycorhizas, but mycorhizas tend to be absent from grassland.
Left: the growing tip of a fungal hypha. Hyphae grow at their
tips. The fungus 'cell' is really a giant cell with many nuclei,
though in some fungi cross-wall partitions occur at intervals
along the hypha. The hypha is surrounded by a hyphal wall.
the growing tip is rich in vesicles, which either bud from the
Golgi apparatus (dictyosomes) if these are present, or else
directly from the endoplasmic reticulum. Many of these
vesicles fuse with the cell-surface membrane at the hyphal tip
and discharge their cargo by exocytosis, which will include
materials to extend the cell wall as the hypha grows. The
vesicles also add to the cell-surface membrane.
Behind this zone is a region of intense metabolic activity -
rich in ribosomes that synthesise proteins and mitochondria
that provide the hypha with power.
Further from the tip, vacuoles of increasing size become
increasingly numerous and large lipid bodies which store fuel.
The middle zone, rich in ribosomes, may be much longer
than illustrated here.
tips. The fungus 'cell' is really a giant cell with many nuclei,
though in some fungi cross-wall partitions occur at intervals
along the hypha. The hypha is surrounded by a hyphal wall.
the growing tip is rich in vesicles, which either bud from the
Golgi apparatus (dictyosomes) if these are present, or else
directly from the endoplasmic reticulum. Many of these
vesicles fuse with the cell-surface membrane at the hyphal tip
and discharge their cargo by exocytosis, which will include
materials to extend the cell wall as the hypha grows. The
vesicles also add to the cell-surface membrane.
Behind this zone is a region of intense metabolic activity -
rich in ribosomes that synthesise proteins and mitochondria
that provide the hypha with power.
Further from the tip, vacuoles of increasing size become
increasingly numerous and large lipid bodies which store fuel.
The middle zone, rich in ribosomes, may be much longer
than illustrated here.
Left: a cross-section through part of
the stipe (stalk) of a mushroom. The
stalk is made up of columns of hyphae,
of variable size, packed together. In
cross-section these hyphae resemble
the parenchyma cells of plants, but in
longitudinal section are shown to be
long filaments, unlike parenchyma, and
so are sometimes called
pseudoparenchyma. This is an
interesting alternative approach to
building a body - building it from
filaments. These sporing or fruiting
bodies, such as toadstools, enable
spores to be released above the
boundary layer of still air that coats
solid surfaces. In air the boundary
layer is generally much thicker than in
flowing water. In water microscopic
filaments or biofilms may be sufficient
to break the boundary layer.
the stipe (stalk) of a mushroom. The
stalk is made up of columns of hyphae,
of variable size, packed together. In
cross-section these hyphae resemble
the parenchyma cells of plants, but in
longitudinal section are shown to be
long filaments, unlike parenchyma, and
so are sometimes called
pseudoparenchyma. This is an
interesting alternative approach to
building a body - building it from
filaments. These sporing or fruiting
bodies, such as toadstools, enable
spores to be released above the
boundary layer of still air that coats
solid surfaces. In air the boundary
layer is generally much thicker than in
flowing water. In water microscopic
filaments or biofilms may be sufficient
to break the boundary layer.
One of the most remarkable things about fungi is their hardiness. Fungi have been able to colonise
extreme environments, such as inside rocks in the extremely cold and dry Antarctic deserts (the driest
places on Earth) and the inside of fuel tanks. Even the mildew that may grow on walls and other damp
surfaces seems to grow well with remarkably little. Many fungi are colonisers, some are adapted to grow
on burnt soil in forests, and their spores will only germinate in high temperatures. Lichens can grow on
bare rocks, even on wind-blasted and salty rocks that line the upper shores. Lichens are remarkable
composite organisms - composed of two very different organisms growing in a single body. One is the
fungus, the other is a photosynthetic cyanobacterium or a eukaryotic alga.
extreme environments, such as inside rocks in the extremely cold and dry Antarctic deserts (the driest
places on Earth) and the inside of fuel tanks. Even the mildew that may grow on walls and other damp
surfaces seems to grow well with remarkably little. Many fungi are colonisers, some are adapted to grow
on burnt soil in forests, and their spores will only germinate in high temperatures. Lichens can grow on
bare rocks, even on wind-blasted and salty rocks that line the upper shores. Lichens are remarkable
composite organisms - composed of two very different organisms growing in a single body. One is the
fungus, the other is a photosynthetic cyanobacterium or a eukaryotic alga.
Above: Daldinia (probably Daldinia concentrica) otherwise known as King Alfred's Cakes. This fungud
grows on ash and occasionally on other deciduous trees. Here it is growing on a fallen branch, which
does look like ash. The sporing body can be up to 5 cm (2 inches) across. Also sporulating on this log
was a myxomycete or plasmodial slime mould.
grows on ash and occasionally on other deciduous trees. Here it is growing on a fallen branch, which
does look like ash. The sporing body can be up to 5 cm (2 inches) across. Also sporulating on this log
was a myxomycete or plasmodial slime mould.
More Fungi
More on fungi coming soon...
More on fungi coming soon...
This bracket fungus, growing on an oak tree, is probably
Ishnoderma resinosum or a related form, as it has the right
shape and colour and characteristically yields drops of red
resin (click photos to enlarge, the droplets are visible as
spots). However, this fungus is said to grow on dead
stumps from September to December, but here it is in June
on a living oak tree. Of course it could be feeding off dead
wood that is part of the tree.
Ishnoderma resinosum or a related form, as it has the right
shape and colour and characteristically yields drops of red
resin (click photos to enlarge, the droplets are visible as
spots). However, this fungus is said to grow on dead
stumps from September to December, but here it is in June
on a living oak tree. Of course it could be feeding off dead
wood that is part of the tree.
