Autumnal walks are crowned by the extravagant hues of the tree canopy along trails where ranks of mystery-shrouded mushrooms and other strange excrescences vie for the hiker’s attention. Fall is the time for the fruiting body of the fungi. That this is so will be explained in good time. Why mushrooms and other fungi are mystery-shrouded is a matter of knowledge; anything unknown encourages human fabrication of myth as explanation. The flame of natural science flickered briefly in the eastern Mediterranean basin several millennia ago; it was squelched by the onslaught of Goths, the harbingers of the aptly named the Dark Ages. Almost a thousand years later, a Florentine lawyer named Petrarch began the search through cloistered libraries for the forgotten manuscripts of the past and became the father of the Renaissance; Italians called it la Rinascita, the Rebirth. Philosophy gave birth to science as natural philosophy with the mathematics that allowed Tycho Brahe’s observations to be used by Kepler to calculate the elliptic orbit of Mars about the Sun in 1604. The physics of Newton, the reformation of Luther and the printing press of Gutenberg ignited the age of enlightenment that burned brightly through the 18th century as a herald of modernity. 
Science at its essence is a search for reason. It is propelled by inquisition and empowered by imagination using a systematic method for establishing what is factual. Over the last two centuries it has expanded exponentially inward to the miniscule atomic realm and outward to the ever-expanding universe and there is much to learn at both ends of the spectrum. At its incipience, the modern age was literally powered by the applied science or engineering of the Industrial Revolution. While the water wheel driven looms of the textile mills mark its onset, it was Newcomen’s steam engine as improved by James Watt that set it in motion. The use of the stored energy of the sun to supplant manpower, horsepower, wind or water is perhaps the most important invention of all time, rivalling fire and wheels in significance. While the law of unintended consequences has yet to become fully manifest in terms of climate, the burning of fossil fuels was the hallmark of the factories of the 19th century, the age of engineering. The mechanization of agriculture precipitated a diaspora from field to factory where manufactured goods created lives of leisure for some. As Edison’s electricity and Ford’s Model T allowed for illumination and transportation, the halls of academia burgeoned in the 20th century; creativity flourished once freed from the drudgery of manual labor. Comprehension of the atomic nature of chemistry and the nuclear nature of physics were the ultimate result 
The notion that matter consists of fundamental units is attributed to the Greek philosopher Democritus in the fourth century BCE; the neologistic atom from the Greek atomus meaning indivisible was his enduring legacy. The alchemy of the Dark and Middle Ages from which chemistry emerged both practically and linguistically concerned mixing different substances, usually to try to make gold or the elixir of perpetual youth. Sweden’s Karl Scheele is considered the first modern chemist, identifying ‘fire air’ as the gas that burned and ‘vitiated air’ as the gas that did not as the two constituents of the atmosphere even though he was preceded in publication by the British Joseph Priestly who is traditionally accredited with the discovery of oxygen which was named by the French Antoine Lavoisier in 1779, an early EEU collaboration of sorts . But homage is due the English school master cum chemist John Dalton (1776-1844) for the fundamental thesis of modern chemistry; chemical compounds exist only in quantitatively consistent proportions. In similar stepwise fashion, cathode rays generated by the passage of electricity through gas led inexorably to the atomic model of Ernest Rutherford in 1909 based on the observation that most particles passed through a thin gold foil, but some were deflected, and some bounced back; the existence of a small, dense and charged nucleus was (correctly) postulated.  Advances in chemistry dominated the first half of the 20th century as the weaponized nitrates of the Haber-Bosch process wreaked havoc in two world wars, ending with the atomic bomb blasts as advent of the nuclear age. The second half for the 20th century was sequentially dominated by the physics of the Cold War that penetrated to the depths of Democritus’s atom, where quarks are joined by the strong nuclear force of gluons to form hadrons. 
Biology will surely dominate the current century. The science of life itself is still reeling from the foundational revelation that transcends the implications of the Christian Bible’s end notes of the same name. Linnaean taxonomy established order out of the chaos of the myriad new species from the Americas by the assignation of genus and species in the 18th century. Darwinian evolution offered a plausible explanation for nature’s endless and beautiful diversity of form that the taxonomy revealed in the nineteenth. The double helix DNA design proposed by Francis Crick and James Watson as “a strange model” that “embodies several unusual features” in the mid-20th century set the stage for the biological Gesamtkunstwerk that has ensued; their initial enthusiasm that “we are not hesitant in being bold” having been more than justified . The original distinction made by Carl von Linné between plants and animals was upended by the magnifying lens. The strange microscopic world of plant-like animals and mobile plants that it revealed was thought to have something to do with origination and was accordingly named Kingdom Protista for its proto-life implications. Magnification eventually reached the cellular level revealing single spherical, cylindrical and helical cells with no nucleus that were called bacteria for the rod shape and named Kingdom Monera for their singularity. That fungi were a wholly separate biological group distinct from plants did not become manifest with magnification; hiding in plain sight, their mysterious machinations eliciting suspicion and aspersion as toad stools 
Fungi were the fifth kingdom after Protista and Monera; not necessarily the last as the biological world is still in flux with DNA blueprints of irrefutable associations that belie appearance. The notion that fungi derived from some type of algae and therefore belonged in the Plant Kingdom is not without merit. Many propagate with root-like structures called hyphae that surround and sometimes embed with plant roots as mycorrhizas. Further reflection and understanding eventually led to the consensus among scientists that fungi were monophyletic – having a single ancestor from which they evolved in new and different non-plant directions – and, most importantly, that they had a unique nutritive mode. Plants are autotrophs, assembling their own hydrocarbon nutrients from sun, air, and water with the photosynthesis processing of chlorophyll. Plants are the producers. Animals are heterotrophs and consume plants or each other by ingestion and digestion. Animals are the consumers. Fungi do neither; they are absorptive, producing enzymes that break down the cellular structures of plants, animals and each other to absorb the decomposed nutrients. Fungi are the reducers. Their evolutionary path has been to embed themselves in their food supply, to maximize the surface area in contact with that food supply, and to form separate reproductive organs to emit spores only when necessary to propagate. Plants produce, animals consume, fungi reduce, and life goes on. 
The word mushroom is of dubious etymological origin. It probably derives from the French mousseron from mousse meaning moss. Perhaps this is due to the dark, dank habitat where mushrooms thrive and mousseron became mushroom as a calque, using existing English words as homonyms for the French. The British are notorious mycophobes and tend to call them toadstools, which may or may not come from the German tode stuhl or death chair (stool can also mean feces to fully invoke the opprobrium). As a matter of further linguistic curiosity, the French word for the ubiquitous white button mushroom is champignon and not mousseron; champs are fields (Paris’s Champs Ėlysées refers to the Elysian Fields, where fallen warriors live in perpetual bliss in Greek – and presumably French mythology). Champignon is also the German word for this mushroom, evidently taken directly from the French; otherwise they are pilz. And to really confuse things, the Latin word for mushroom is fungus, which in turn derives from the Greek spongos, or sponge. Presumably, the Greek familiarity with marine sponges suggested an association based on form and function as both are fibrous, compartmentalized, and “spongy.” And since fungus is a Greek word, the plural is fungi, pronounced fun j-eye; there is no such thing as a fun guy. 
The reproductive or fruiting bodies of fungi are generically called mushrooms even though they have a variety of forms that bear no resemblance to an umbrella; some are quite bizarre and exemplify the creativity of evolutionary pressures in pushing the envelope of credulity. The elegant stinkhorn (Mutinus elegans) looks like and is also commonly called the dog penis that it resembles; it creates a gelatinous and fetid (stinky) slime that attracts insects to do its spore dispersal bidding. There are fungi that grow on dead trees and look something like the ears of Tolkien’s ents; they are called tree ears in both English and Latin (Auricularia auricula). Perhaps the most disturbingly eerie are the club-shaped, gnarly, white-gray cylinders that project in clusters from the ground, almost as if an animated corpse is struggling to escape internment; they are morbidly called dead man’s fingers (Xylaria polymorpha). Hopefully one would not find these adjacent to a skull-shaped puffball (Calvatia craniformus) as further evidence of Edgar Allen Poe’s macabre tale of premature burial. There are coral shaped fungi with delicate shades of mauve and yellow, black and citron blobs of jelly, giant rosettes of overlapping plates, a hen-of-the-woods that looks like a brooding chicken, and an old-man-of-the-woods that doesn’t look like a homunculus. Even though the mushroom is just one fungus morphology, the two words are and will continue to be used as synonyms in common parlance. Mushrooms are what the hiker will encounter and that is what will be addressed hereafter, excluding the yeasts, molds, rusts and other fungal variants only out of necessity of textual scope. 
The term fruiting body to describe a mushroom is not scientific jargon but rather a practical and descriptive analogy to plants. Apples are the fruit of apple trees and contain the seeds for its propagation; plants employ the motility of hungry animals by making apples sweet and red. Mushrooms are the fruit of the fungus that contains the spores mostly to be wafted away by the wind but in some cases carried off by animals like the flies drawn to stinkhorns. The apple tree lives on long after the apple is either picked or falls to the ground uneaten just as the fungus lives on long after its mushrooms have fulfilled their reproductive mission. The apple will produce new apples in subsequent seasons just as the fungus will create new mushrooms according to its reproductive needs. Since the fruiting body of the fungus was the only part recognizable by early botanists at the incipience of biological organization, they are sometimes called macrofungi for this reason, fungal taxonomy has traditionally and somewhat misleadingly been characterized almost wholly by these ephemeral growths and not on the actual subterranean and secluded fungus that lurks below in unobservable tangles called mycelia. One consequence is that DNA sequence-based biology is wreaking havoc with the extant taxonomy which was based on morphology since many fungi that look alike aren’t even distant cousins.
The mystifying, spontaneous emergence of mushrooms after rain is so notable that the very term “to mushroom” suggests explosive growth (both before and after the advent of the atomic bomb cloud of the same name). To understand why this is so, it is necessary to delve into the recondite realm of spores, hyphae and mycelia. One reason that mushrooms have caps is so that the spores which are located on small club-like structures called basidia attached to the gills under the cap are afforded the necessary humid environment needed for spore ejection. The actual mechanism is called surface tension catapult and accelerates the spore at 25,000 g’s to a speed of one meter per second in one microsecond over a distance of one millimeter, about midway between the gills. When the spores are ejected, the wind carries them to new habitats. When a spore lands in an auspicious locale, it will germinate, sending out an initial filament called a hypha that will branch repeatedly to create a fibrous mass called a mycelium.  The mycelium is the corpus of the fungus (dead man’s fingers?). It is as elusive to the casual hiker as are the roots of a tree; the hyphae are interwoven into the soil and detritus of the forest floor or intermingled with roots as previously discussed and are thus almost entirely hypogeal, the forest unseen. Mycelia can grow to gargantuan proportions, limited only by the extent of a nutritive ecosystem. The largest living organism in the world at present is a honey mushroom mycelium (Armillaria ostoyae) that occupies about two thousand acres in the Malheur National Forest in eastern Oregon and weighs 600 tons, the origin of the apothegm humungous fungus. 
The mycelium that results from a single spore in many cases requires a suitable mate to make a mushroom; two compatible hyphae growing from two compatible spores are needed. It is analogous to the male and the female genders of most plants and animals and is called heterothallism. But with many fungi, it is much more complicated, as there are a lot more pairing possibilities. There has been limited study in this area due to the difficulty in distinguishing different hyphae based on appearance. Understanding pair-wise behavior is dependent on a large number of tedious empirical observations. What testing has been done has shown that there are as many as 20,000 pairing combinations in some mushrooms. Each hypha brings one nucleus to the union, creating a cell with two nuclei, called a dikaryon. In this combined form, the mycelium grows, taking its nourishment from a variety of organic sources. Mushrooms form from the dikaryon mycelium by coalescing into a denser fibrous mass known as a primordium. The structure of the mushroom is established in embryonic form with a distinct cap and stem, poised in the mycelium for the appropriate environmental stimulus. After a rain, water permeates the ground and the inchoate mushroom absorbs it, expanding rapidly with the preexisting structure now enlarged by the addition of the fluid (mushrooms are about 95 percent water). This is why mushrooms pop out of the ground overnight after a rain. The moisture trigger is also relevant to the propagation of the species, as the mushroom will open and release its spores when environmental conditions are likely to favor their successful incubation. 
The cryptic introductory alliteration “fall is the time for the fruiting body of the fungi” should now be as resonant as April showers bring May flowers. Flowers are necessary for the fruits of fall to spread seeds wintering over to await the renaissance of spring. Mushrooms are necessary for a fungus to spread its spores of succession. Fall marks the diminution of the summer’s photosynthetic assimilation of solar energy built up in plant roots to provide nutrition for everything else, fungi included. It takes energy to make a mushroom and the energy thus consumed is no longer available for growth, the essence of life. Fall marks the onset of winter’s waiting when growth slows to a stop. Fall is the time of fruit and fungal fruiting bodies for the same reason. Mushrooms are among the most notable features of any autumnal woodland trail. They come in many sizes, shapes and colors as solitary sentinels or clustered in ranks on a log. Some are beguiling like the white-dotted crimson cap of the Fly Agaric (Amanita muscaria), the archetypical mushroom of tchotchkes and playpens. Some are edible like the Meadow Mushroom (Agaricus campestris), grandparent of the Portabella with an unfortunate doppelgänger that kills, the Destroying Angel (Amanita bisporigera). Some are medicinal like Turkey Tails (Trametes versicolor) that feather dead logs from one end to the other as if trying to take flight.
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