SHOULD THE ALMIGHTY VISIT ME and tell me that He had decided to destroy from the face of the planet all groups of living things but one, and He told me to choose which should remain, I would not hesitate for a second — let the fungi live! My first real job was selling newspapers on a street corner. (I don't class pulling out dandelions at the age of seven for the new neighbors over the road as a real job.) My second was as a laboratory assistant in the botany department of Melbourne University where I was assigned the task of maintaining the fungi cultures — to regularly transfer tiny blobs of fungus from old test tubes into new tubes filled with a fresh supply of nutritive media, and to keep an ever-watchful eye open for public enemy number one of all fungus growers, mites. That's when I fell in love with this mind-blowing branch of life's universe. Or maybe it was childhood exposure to Rupert the bear stories that did it; barely a scene in the early series lacked a fly agaric or its like.
True, fungi are sometimes associated with crippling plant (and occasionally animal) disease. The majestic, all-American tree, the American chestnut, that once made up a full quarter of the hardwood trees in its natural range, was brought to its knees during the first half of the twentieth century by a mere fungus, Cryphonectria parasitica. But you know something; chestnuts had survived for many thousands or millions of years before the arrival of the white man. Did we do something wrong? Should we have known better? One cannot help but wonder if this death-dealing blight might never have occurred had we observed biblical laws; but that's another matter. Anyway, why pin the blame on the fungus? And besides, some hopeful signs are emerging to suggest that, with a little help from man, they may recover.
The positive side of the ledger far outweighs the negative. Unlike green plants, fungi are unable to build structural materials from simple chemical compounds like carbon dioxide and water by using energy from the sun. In other words, they can't photosynthesize. Like animals they must, therefore, live on organic material from other living things, whether alive or dead. This need lies at the heart of their immeasurable value in the great scheme of life. Together with bacteria, they make the perpetuation of life possible by decomposing the remains of living organisms. They do this to get at the chemical energy supply locked up in the dead tissues. In the process, as they break down complex, energy-rich chemical compounds, they release nutrients for re-use by plants. Without these two groups to recycle earth's nutrients, the scant supply of some of them would long ago have been exhausted, locked up in a thick layer of corpses, finger nail clippings, dried leaves, and dead trees littering the ground.
Some fungi don't wait around for a plant or animal to die before chiseling away at its energy supply. “Killer fungi” are known that attack creatures as large as insects and spiders. Some secrete an adhesive substance, a kind of natural flypaper, that traps unwary passersby. Later, a fungal hypha (see below) grows into the victim and digests out its nutrients. Other soil fungi come adorned with tiny lassos that tighten around any nematode that happens to blunder into them. Amazingly, these fungi will not sprout a lasso unless the soil contains suitable nematode prey. The “stupid” worms seem to seal their own fate by producing an unknown substance that tells the fungus that dinner is coming. Ah, the mind of God. A number of species of fungi produce spores that, should they land on a suitable insect, such as an ant or a caterpillar, somehow find their way through its tough exterior and feast on the insect's tissues. Later we will talk about a remarkable fungus that “harpoons” its victims. Remember, such remarkable dramas are going on all around us. If only we had the eyes to see.
Getting back to the value of fungi in nature, we cannot bypass another vital role played by fungi in plant nutrition. Many, if not most, plants require the services of some kind of fungus, in what is called a mycorrhizal association, to jump start the workings of their roots, enabling them to soak up nutrients from the soil. Let Ecos, January-March, 1999, explain:
The hyphae act as an extension of the plant's root system, delving into soil pores too small for the comparatively clumsy roots to penetrate. They capture vital resources such as phosphorus, trace elements and water and channel them to the plant. Scientists also suspect that mycorrhizas help protect plants from fungal diseases, partly by occupying the space that a pathogen might otherwise exploit, partly by enhancing plant fitness through increased nutrient uptake, and partly by responding antagonistically to the arrival of such organisms.
Of course, the arrangement is not one-sided. In return, the fungus helps itself to the carbohydrates circulating through the root tissue.
In the majority of fungi, by far the greatest part of a fungus, called the “mycelium”, remains unseen beneath the surface of the growing medium, be it woodland soil or shoe leather. The larger, visible parts (such as mushrooms) are merely the reproductive organs, or fruiting bodies of the fungus. The mycelium consists of a tangled network of narrow, tubular threads, called “hyphae” (singular, hypha), which extend in all directions, secreting enzymes to break down organic materials into simpler substances that can be used as food. The breakdown products are absorbed into the hyphae along with vital mineral salts and water. Exactly what chemical foodstuffs are needed by any particular kind of fungus remains often a mystery, much to the chagrin of those who would love to raise certain kinds of delectable fungi for market.
The visible fruiting bodies also consist of masses of hyphae, but in this case, instead of growing in an apparently random way, they grow in an organized fashion. The stalk of a mushroom or toadstool, for instance, consists of thousands of strands of hyphae packed together in parallel, just like the many wires that make up a cable. The sheer size of a mycelium can take one's breath away. In October, 2004, scientists discovered in Switzerland what they believe is the largest ever found. At one thousand years old, and with the diameter of 8 football fields, it covers 35 hectares in area.
However, not all fungi have hyphae. Some, such as the yeasts, consist of single cells that go about their business all by themselves.
Although the mycelium is perhaps the most important part of a fungus, it does not vary much from one species to another. At least not in looks. There is great variation at the biochemical level. As a result, the classification of fungi is based largely on their reproductive structures, which are much more diverse. In fact, the variations seem endless to our limited minds. Fungi reproduce both sexually and asexually. Based on the method of their sexual reproduction, fungi are divided into three classes — wait for it — Phycomycetes , Ascomycetes and Basidiomycetes. The differences between these classes will have to wait for later articles to explain.
A fourth class, the Deuteromycetes (also called “Fungi Imperfecti”), do not appear to reproduce sexually. However, many fungus experts, known as mycologists, believe that this is simply due to the fact that their sexual reproductive structures have not yet been discovered. It is the desire of aspiring mycologists to discover such sexual fruiting bodies. The author remembers well, while working as a laboratory assistant in the fungus department of Melbourne University, assisting a graduate student in his endless quest for such a fruiting body from one species. Countless specimens of a particular species were cultivated under differing conditions, then sliced up and examined under the microscope in the search for the elusive sexual fruiting body. Alas, 'twas not found.
Fungi, fungi everywhere
From the bright red Fly Agaric toadstool to the mould growing on an old boot, fungi can be found in practically every environment, some of them quite inconceivable to us, where life is possible. At least 250,000 species share our planet with us. There are even fungi that live at the interface between water and kerosene, somehow “decomposing” the kerosene. In World War Two one fungus caused problems for Pacific armies — it ate into the glass of binoculars, rendering them practically useless.
My favorite example of fungi that live in one of those inconceivable fungi habitats is the order Laboulbeniales. They are tiny, specialized parasites of insects and arachnids (spiders, mites and scorpions) that occupy bizarre parts of the anatomy. Rarely seen because of their size, they are in fact common. Any ant hill would contain specimens of infected ants. Many Laboulbeniales are species specific — that is, they are found on only one species of host. More strangely, they are restricted to very specific parts of their host — a leg, or one antenna, for instance. One species is only ever found on the fifth segment of the left hind leg of the males of one species of water beetle! Every time I think of them I'm sure I hear a faint chuckle from heaven.
I love fungi not only for their bizarre and endlessly fascinating and varied ways of making a living and perpetuating their kind but also for their raw beauty. Who can fail to be stirred at the sight of the colorful array of graceful toadstools, bracket fungi, coral fungi, morels and their ilk that pop up as if by magic after an autumn soaker?
Don't allow any prejudices against "pernicious toadstools" bar you from looking further into this amazing universe of often-hidden organisms. Without fungi you would not be able to enjoy that much-loved glass of wine or beer. Or the unique flavor of blue cheese. In fact, you wouldn't have anything to eat, for reasons already explained. Once again, God has given a vitally important part to play in the story of life to a most unassuming cast of nothings. Let's be humbled by the fact that our lives are made possible, and greatly enriched, by something we hardly ever give even the briefest thought to. Let's rectify that travesty of justice right now as we recount the story of just a few of the many thousands of different kinds of fungus.
Every morning throughout much of the year, about 9 AM, practically every cow paddock in the world is the scene of unseen fireworks. At about that time, freshly dropped dung pads serve as the deck from which Pilobolus “cannons” fire their miniature cannonballs. For this reason it is sometimes called the shotgun fungus. The entire cannon grows up over the course of a few hours in the morning hours, during which time it cocks itself by a complex set of biochemical reactions that produce a buildup of pressure which results in a forceful discharge of its sporangium, or spore-bearing capsule. The cannon is very sensitive to light and is capable of aiming its capsule with “enough accuracy to strike within 3 to 5 mm of a point light source” (James & Kylander 1982, p. 19).
As always, a picture is worth… As you can see from the photo, the swollen tip carries a small black pellet at its apex — the sporangium. When the cannon fires, the sporangium can shoot up to a height of six feet (1.8 meters). Yet the entire shooting apparatus is barely a centimeter high!
Living ballistic missiles
Ponds and puddles across North America provide the setting of one of nature's many spectacular dramas — plants shooting animals. The animals are rotifers, microscopic swimmers that browse on bacteria. The plants are tiny fungi, each armed with an elongated cell shaped like a gun barrel. And the gun is loaded.
When a rotifer bumps against one of these armed plants, it triggers a violent reaction. The fungus quickly fires a speck of cellular matter at the intruder, blasting a hole through the rotifer's outer covering. Then the plant pushes a needle-like probe through the wound and injects a spore into the rotifer's body. The spore rapidly multiplies into a number of spores which, when sufficiently mature, stream out of the animal host to hunt their own prey.
What man would ever come up with a scenario like that — a microscopic shootout, in which the pistol-packing aggressor is a plant, and its victim an animal? Most people would not have believed it conceivable. But in 1981, “ Mycologia ”, the authoritative journal of all things fungoid, published a paper by G.L. Barron which would convince even the most diehard skeptics. Of course, believers should not be surprised, as they know there is no limit to God's ingenuity.
The fungus goes by the romantic name of Haptoglossa mirabilis. Most appropriately, Haptoglossa looks a little bit like a miniature cannon. Electron microscope studies confirm just how fitting this is. They show clearly the presence of a gun-like bore and a complex harpoon-like attack apparatus in the parasite.
In the natural state, Haptoglossa lie in wait, with the base of their cannon securely fastened to a soil or sand grain by means of an adhesive pad. The barrel is raised at an angle to the substrate to increase chances of a fruitful encounter of the unusual kind. Swimming around in the same environment are numerous rotifers, completely oblivious to the potential hazards lurking around them. According to eyewitness accounts, if an unsuspecting rotifer strays too close to one of these living blunderbusses, it comes to a sudden stop, then writhes and struggles furiously. Obviously, the gun-toting fungus has fired, and impaled the rotifer on its spear-like extension. The adhesive power of the base pad anchoring the fungus to the substrate is sufficiently strong to temporarily hold a struggling rotifer. Within thirty seconds, though, the rotifer will pull free.
Understand that the fungus is not skewering the rotifer with a view to eating it itself. What it is actually doing is extending an unrefusable invitation to the animalcule to become the nursery of future Haptoglossa fungi. If the rotifer could know what was going on, it would certainly not accept such an invitation, because its flesh will become the food that the "baby" fungi will feed on. What has actually happened is that the fungus has fired its germ cell into the rotifer. This germ cell grows at the expense of its victim. By the time the fungal spores are ready to be released, the rotifer is a tiny wee bit dead.
Naturally, we have given here a very simple account of something that is extremely complex. Mycologists don't understand the mechanism of firing. A number of them agree that it probably has something to do with osmotic forces, and rupturing along precise lines of predetermined weakness. One day we will all understand it fully, right down to the last mathematical formula. For the time being it is sufficient for us to see in this another example of the glory of God that fills the earth.
One must not imagine that God's genius for infecting rotifers by fungi was exhausted with the explosive mechanism of Haptoglossa. The same author published an article in the Canadian Journal of Botany describing another newly-discovered fungal parasite of rotifers named Tolypocladium trigonosporum (I'm sorry, but there is nothing I can do about that). How the infective spores of Tolypocladium gained entry into its victims is not mentioned. Possibly it was ingested by the rotifer during normal feeding activity.
Haptoglossa forms its vicious little infective spores within the body of its host. These spores escape through an evacuation tube, swim around for a while by means of whip-like flagellae, settle and encyst, then almost immediately germinate to produce an injection cell. Tolypocladium, by contrast, produces its new agents of infection on the tips of fertile hyphae that break out through the tough case of the dead rotifer.
Bird's nest fungi
They are a fungus, but you wouldn't know it. They are only a few millimeters high, but contained within these minute hunks of life is a universe of fascination. They are cup-shaped, and contain a number of small, hard, lentil-shaped "eggs" neatly arranged within. Which is why they are called "bird's-nest fungi".
Who knows what our ancestors must have thought they were? Did Solomon have them figured out? (I Kings 4:33) If he did, he scooped us moderns by many centuries. Because until 1790 they were thought to be flowering plants, the little "eggs" being seeds (Dickinson & Lucas 1979, p. 33). And it was not until 1951 that a man by the name of Brodie described how the "eggs" fly from the nest (Alexopolous 1952, p. 527). (Rather strange, isn't it? Usually eggs have to hatch before they fly.)
But fly they do. In the 1940's, a devoted mycologist placed some of these little "nests", eggs intact, on the ground under a Juneberry bush. About a month later he discovered some of the eggs were missing. In true Sherlock Holmes style he searched till he found a number of the little "eggs" hanging by stringy threads up to three inches long (75 mm) from leaves above the "nests".
The mystery was how. Brodie solved it. Pursuit of a theory showed the answer. But before we cut the suspense, let's consider these little nests and their eggs briefly. The "nests" are actually fruiting bodies of a Basidiomycete (one of the four major groups of fungi) fungus. The "eggs" are peridioles, which are a special kind of spore-containing chamber of certain Basidiomycetes. Inside the peridioles are masses of basidisopores — the "seeds" of the fungus. The peridioles, several per cup, are attached to the inside of the cup by means of a slender mycelial connection called a funiculus. When wet, the funiculus expands greatly and may even reach a length, when stretched, of 6 to 8 inches (15 - 20 cm). Under such conditions the very base of the cord, the hapteron, becomes very sticky, and will adhere to just about anything it touches. Does this fact give you a clue as to how the peridioles fly from the nest?
For years, many people who studied this fascinating fungus, thought that the peridioles must have been shot into the air by some explosive force generated by the fungus itself. This was no idle speculation, as other fungi exist which do just that. But numerous experiments failed to detect any such explosive mechanism.
Some then turned their thoughts to animals. Could a passing animal somehow pick up a peridiole as it brushed past the nest? But a close inspection of the fungus ruled this out. The geometry of the cups and the elaborate attachments on the peridioles suggested that a precise and elaborate mechanism for spore dispersal was involved (Dickinson & Lucas, p. 33). Have you guessed it yet? Remember, it has something to do with wetness.
Well, let's hold you in suspense no longer. Brodie discovered, as a number had begun to suspect, that the cups of the bird's-nest fungi are so constructed, with the precise geometry needed, as to act as splash-cups from which raindrops, coming in at a velocity of about 18 feet (6 meters) per second during a heavy storm, hurl out the peridioles to a distance of 3 to 4 feet (one meter). Some of the momentum of the raindrops is transferred to the peridioles, as when a moving billiard ball passes on some of its momentum to another upon striking it.
The force of ejection causes that portion of the funiculus called the "purse" to burst and release the funicular cord and hapteron. The now-wet and thus now-sticky hapteron sticks fast to any solid object it touches as it hurtles through space. When it does stick, the funicular cord stretches then elastically contracts, winding around and around whatever object it hits. This all takes place, of course, extremely rapidly.
Thus the peridiole, with its dose of spores, is in a position to either release its spores to the wind as the peridiole disintegrates, or it may be eaten by an animal. Those that are eaten by animals pass through the gut unharmed and usually end up growing on the dung pad.
Who can fail to see brilliant design in this? Many do. The faith of evolution is surely a great faith. Many are determined to see chance as the brains behind the design of these fungi. As Dickinson and Lucas put it:
The bird's-nest fungi are of little economic importance… but they exert a great fascination for many botanists. The superb adaptation of many of their species to this splash method of spore dispersal implies a marvelous degree of evolutionary perfection. Every feature is tailored to this operation. The way they are attached to the substrate, their aspect, the angle and texture of their walls and, of course, the amazing peridiole tails, all increase the chances of successful spore dispersal ( p. 33).
Let's give God the credit, not natural selection.
References and notes
Alexopolous, C. J. 1952, Introductory Mycology, John Wiley & Sons, Inc., New York
Dickinson, C., and Lucas, J. 1979, The Encyclopaedia of Mushrooms, G. P. Putnam's Sons, New York
James, D. E., and Kylander, J. E. 1982, Culturing Bacteria and Fungi, Carolina Biological Supply Company
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