by Guy Murchie
You might think hot springs an unlikely home for any vegetation, but green plants often grow in water as hot as 145°F. and pale ones without chlorophyll up to 162°F., while at least one hardy veteran, Osciliatoria, a blue-green alga perhaps little changed since the earth's early days, is reported to thrive in alkaline, silica-charged springs as hot as 194°F., and an extraordinarily tough breed of bacteria indigenous to deep oil-well brines sometimes lives even above the boiling point, 212°F.
Dry heat is a more normal problem, and plants survive in deserts mainly by either conserving their moisture or dying away to mere dry seeds that sprout only when it rains. Succulents store water in ingenious ways: the century plant in its leaves, the night-blooming cereus in underground bulbs, the cactus in its fat stem. Others, like the agave, hopefully leave their gutter-shaped leaves continuously open to catch the rare rain, the exact opposite of rainy-area plants like Sarracenia minor that wear perpetual hooded "umbrellas" to defend them from the too frequent downpours.
The giant saguaro of the American desert is perhaps the most dramatic example of a drought-resistant tree. Unlike the spindly mesquite, whose roots drill deep downward to sip continuously from whatever water may be under the desert, the portly saguaro puts its whole faith in a wide, shallow, lacy network of root that has been growing for perhaps 200 years but has no hope for a drink except when it rains. Since the saguaro is bulky, tight-skinned, sometimes more than 50 feet high and capable of holding 30 tons of liquid, it can wait comfortably through several years of drought if need be and, upon a sudden downpour, gulp up tons of rain in an hour, perhaps reaching saturation within half a day, which means being more than 90 percent water. American desert Indians not only found this bountiful plant a vital water resource and mashed it to extract the bitter liquid during extreme droughts, but they regularly ate its melonlike fruit, cooked it into a syrupy preserve, fermented the juice for "wine," pounded the seeds to "butter" and used the remaining long stems as lodge poles, the leftover scraps as firewood.
Quite insignificant by comparison appears the little patch of lichen covering a weathered stone. It is scarcely a fifth of an inch thick and has no obvious rain reservoirs, yet it can survive drought for twenty times as long as the saguaro, stoically waiting in a dormant state - in one recorded case for 87 years! - until water instantly reawakens it to active growth. The only plants I've heard of that can get along completely without rain (or root water) are the American pygmy cedar (Peucephyllurn) and the Saharan caper plant (Capparis spinosa), which keep green and healthy under extreme drought conditions just on the humidity they absorb from night air.
The way most plants cope with the onset of a cold winter is to retire into a state of hibernation. In doing so, trees that are not evergreen may almost completely dispense with chlorophyll, photosynthesis and evaporation by shedding their leaves, breathing only feebly through bark and buds, and hardly metabolizing or growing at all. Although severe cold spells may have frozen their sap solid and its consequent expansion combined with wintry winds may have cracked their brittle wood to fill the sap channels with air bubbles, happily the coming of spring has a way of correcting the damage by creating new sap tubes and priming them with fresh bubble-free sap or, in the case of certain trees and vines (birch, maple, grape ... .), vernal root pressure has been known to force new sap into some of the old air-filled tubes as well.
Many smaller plants on the other hand, evidently finding hibernation too difficult or wasteful as a winter strategy, take the more drastic step, in a greater or lesser degree, of dying. Thus they save the energy it would require to keep going all through the cold months and, if they are annuals, their seeds can still sprout and carry on in spring or, if perennials, their roots expectably "come alive" with the season. This way of wintering, in case you like the philosopher's perspective, is a demonstration of one of the advantages of death, a subject we will explore in some depth in Chapter 20.
STORAGE
Do plants store up any reserves of nourishment to tide them over a drought? Do they have anything to compare with an animal's stomach or stomachs or surplus layers of fat? Yes, plants often stash their food or fuel in special reservoirs in their leaves, bulbs and stems. An onion, for example, is really a head of leaves that adapted itself to hoarding plant food. A potato is a stem that evolved a belly for starch. The acrocomia is a tall palm that has done the same with a bulging paunch up to 17 feet in girth. The kapok can be a portly tree 20 feet high under ideal cultivation, although it grows skinny and 100 feet high when it must compete for sunlight in a rain forest. The baobab is the fattest of all trees, often exceeding 100 feet in circumference though only 40 feet high and, being soft and pulpy inside, is a favorite food of African elephants who, if they get the chance, will knock it down and consume it completely! The creeping cashew of the Amazon valley, on the other hand, looks like a shrub, but actually has a huge secret trunk that it conceals underground as it circumvents its rivals by living like an iceberg: eight ninths out of sight.
Many flowers, even dainty ones, have also made their place in the world by evolving into giants, increasing both their appetites and their storage capacities over millions of years until they have turned into hungry monsters, like a rain forest "violet" that now sometimes hulks as big as a plum tree, a "milkwort" that twines upward 100 feet and more, a rose from which arose hawthorn and apple trees, a pea that evolved giant locust trees, lilies that turned into the Joshua trees of California, and the aforementioned Dragon Tree of Tenerife. Then there are the 120-foot bamboos of southeast Asia, which are really overgrown members of the ancient family of grasses, a sunflower 30 feet high in the Galapagos, a bignonia that became the catalpa tree, a giant "verbena" that resembles a horse chestnut tree, a species of 60 foot tree ferns of Tahiti, tree lobelias, tree heathers, tree cabbages, tree geraniums and finally the gargantuan groundsels of Mount Kilimanjaro that are in fact 20-foot cousins of daisies supported on stems 4 feet thick. Although all trees must ultimately have evolved from something much smaller, it is more than possible that these big brothers of our little friends may today only be in passing phases of gigantism that will eventually evolve back toward temperance and lowliness, just as the heirs of club moss trees that towered 90 feet high and 5 feet thick in the coal ages now stand only a few inches tall.
I suppose the simplest and smallest of vegetables (not counting viruses) are bacteria. But they, not being given to paunches, have solved their storage problem differently by evolving tastes for foods that would likely be plentiful even in a drought or a famine. Thus some kinds of bacteria have acquired an appetite for hydrogen sulfide (rotten-egg gas) and now use it instead of water in photosynthesis, which makes them exhale sulfur instead of oxygen. Certain other bacteria meantime have learned to live on ammonia found in decaying tissues, on hydrogen, methane or even on iron, oxidizing each of these inorganic foods to build themselves carbohydrates not with light energy, as in photosynthesis, but with chemical energy in the alternate process known as chemosynthesis.
FUNGI
No doubt the most successful near relatives of bacteria are molds and yeasts, which are classes within the subphylum called fungi. But as fungi have no chlorophyll of their own, they rely (as we do) on the photosynthesis of others, and their tastes have proliferated accordingly. So, starting with leavened bread and fermented wine, they can live on almost any vegetables (including fungi), meat and fish (dead or alive), cheeses, jams, sauces, etc., then paper, ink, books, cloth, leather, bone, dung, soil, wax, wood (including living trees), wool, upholstery, girdles, glue, paint, creosote, rubber, asphalt, plastics - and a few even on things like copper salt and glass - almost anything but metal.
In other words, fungi are about as unfussy as eaters can get and therefore are among the best adjusted organisms on Earth. it is true that humans are inclined to think of them as coming from the other side of the biological tracks but, before we drop them from the register, let's remember that we too depend utterly on the chlorophyll of oth
er creatures, we too ferment the food we eat and we too stop at almost nothing in our search for diverse edibles from spaghetti, corn flakes, seaweed, opium, coffee, vodka, bird's-nest soup and blazing plum pudding to quinine, vitamin pills, canned rattlesnake and chocolate-covered ants. While man is a new and single, experimental species of unproven stability who cannot refrain from flirting with massive self-destruction, the fungi have been solidly established on Earth several hundred times as long and are now sensibly diversified into nearly 100,000 species that live in the ocean, throughout the soil, on all lands (including glaciers) and whose invisible spores float everywhere in the air and to some degree through space.
Such success of course is partly due to simplicity and to modesty of aim. Fungi avoid headaches, stomachaches, toothaches and heartaches by just not having any heads, stomachs, teeth or hearts. Instead of private or internal digestion, for instance, they use a public, external system and rather than eat first and digest afterward, as we do, they digest first before even deciding whether the meal is worth eating - the "proof," so to say, coming before the "pudding"! This is possible because the body of a fungus is primarily a branching meshwork of microscopic filaments called mycelia, whose long cells grow at their tips so fast you can actually see them snaking across the field of a microscope, and they are continuously exuding enzymes that disintegrate or digest everything edible (often 100 percent of solid matter) within reach, later consuming what they can of it at leisure. The filaments may be as fine as one one-hundred-thousandth of an inch in diameter, but they put out side branches about every half hour, and thus a single spore multiplying into cells can add up to a total length of hundreds of miles in two days' growth.
Although most fungi prefer a moist climate of around 80°F. and get sluggish when it is dry or cold, you can't kill them by freezing, because they readily hibernate and wait confidently for warmer times. A few species, on the other hand, like it hot and grow so lustily in summer that they generate heat above 130°F. in grain elevators, sometimes stimulating heat-loving strains of bacteria to multiply so fast the temperature rises to the bacteria's limit of about 170°F., whereupon chemical oxidation, if conditions are right for it, will cook the fusty, fuming ferment to the smoldering point at which it may "spontaneously" burst into flames.
LICHEN
Where fungi have made their most important mark, I would think, is in their constructive associations with other organisms. Lichen, for example, is a very ancient and proven partnership between fungi and algae. Evidently it began casually some 350 million years ago when algae were trying to broaden their beachhead on dry land and fungi were casting about for handy green vegetables to eat, or it may have happened earlier when both were still completely at sea. Either way, the tough active fungi seem to have taken over the gentle algae cells like farmers who herd cows, gradually discovering how to weave tight corrals of mycelium around them while "milking" them of their sweet, photosynthetic juices, at the same time rewarding them with protection from sun, weather and enemies while munificently bestowing the obvious benefits of travel without removing the basic comforts of home. Although some 15,000 "species" of lichen are already recognized, each is more specifically classified as an established combination of a species of fungus and its own completely domesticated species of alga. Experiments have shown that it is possible for the fungus-and alga to live apart in a fashion when forcibly separated, but the operation is about as ticklish as depriving a farmer of his favorite cows. The fungus is apt to go hungry and the alga risks being dried up or washed away with the changing moods of the weather while both partners obviously "yearn" to get together again. The fungus generally assumes the role of "husband" in this remarkable symbiotic "marriage," but there are also a good many cases (as among humans) where "she" manages to dominate "him" both in size and strength. Whoever wears the pants, however, it is virtually always a satisfactory union even to the point of having offspring, who are begotten not sexually but by simple division as small crumbs of lichen (alga cells enclosed in mycelium) break loose from the parent body, often to be wafted aloft on the wind and to float great distances in a more or less dormant state before alighting on some bleak crag or arctic scree, where a little moisture may induce them to shoot out new filaments to secure a grip before they are blown away again to a fate unknown.
The only other symbiotic partnership of fungi and green plants I can think of that may be more important than lichen is the curious union between fungi and the roots of evergreen trees. It's known as mycorrhiza, and occurs when the roots go exploring, almost calling, through the ground for vital minerals, an act that provokes the ground in return to arise and answer the roots in the form of the invisible threads of fungus containing those very minerals - all because the fungus too is hungry, in this case hungry for the energy obtainable only from the roots of those same sunlight-absorbing evergreen plants above them. Which is why nurseries sell pines and spruces with burlapped balls of earth around their roots: so they will be assured the fungi partners they need to survive.
SEEDS
We cannot end a chapter about the vegetable kingdom without saying something about seeds. Because although the kingdom got along without them until about 350 million years ago, when evolution devised its first one, the seed is now well established as nature's best all-around invention for starting vegetation in new places. It also possesses a world-changing power that is truly mystic in the sense that it can potentially reproduce not only the complete tree or plant it came from, but all the trees that can descend from that one, indeed (if conditions are favorable) whole forests of them, including those that will eventually mutate into new species - and evolve into higher forms of life, ultimately (in billions of years) permeating all the kingdoms without any known limit.
In other ways too, the seed is not the simple thing it seems. Nor is it the beginning of a new plant, which normally is conceived when an ovule is fertilized by a grain of pollen. For the fertilized ovule has to grow for many days to become a seed. A seed thus is a sort of vegetable egg, a partly developed organism in a protective shell with all the food it expectably needs until it can forage for itself in the outside world.
On the average seeds are the size of a grain of wheat or rice, but a few of them go to extremes and become hulking 80-pound coconuts on the Seychelle Islands or invisible specks of orchid "dust," of which it takes 8 million to weigh an ounce. They may be of almost any color, and of a great variety of shapes, from the sphere of the black nightshade, the ovoid of the bean and the lens of the lentil to the disk of tulip, the star of puncture vine, the javelin of oat, the torpedo of mangrove, the tusks of devil's-claw, the propeller blade of maple, the glider of zanonia, the feather of clematis and the parachute of dandelion.
It is understandable that much of a plant's energy goes into seed production, for upon the seed depends the whole future of its kind and, to a large degree, of all the animals that feed on (and therefore distribute) that seed. The flower that preceded it obviously evolved to make sure the ovule got fertilized to start growing the seed. The fruit that followed evidently appeared as a home for the seed and often also a vehicle to carry it to its destination. Inside the seed meanwhile a tiny, new, unseen plant takes shape, forming a stem, a root and the beginning of leaves, all neatly stowed with nourishing starch in the armored and sealed container, The twin halves of a peanut are a familiar example of the two first leaves of an unborn plant. When the seed has attained the fullness of seedhood, however, it stops developing and goes to sleep to await "G-day," its germination date, its mysterious time of appointment with the outside world. In the vegetable kingdom, you see, the gestation period for seeds is not regular and they rarely hatch open on a predictable schedule but instead must await a number of conditions, presumably to allow time for dissemination.
Dissemination means literally "outward sowing," which well expresses seeds' evident eagerness to travel. I am not thinking just of the modest ones like violet seeds, whose pod bursts like a tiny popgun, s
hooting them a few feet to possible fresh ground, but also of the tufted seeds of milkweed, thistledown or willow silk that ride the breezes, tumbleweed included, and of those who prefer to hook themselves a ride on a passerby, like the grapple plant that catches hold of moving paws and hoofs, like the burdock that clings to any fabric with its now-patented (Velcro) brand of fastener action, and the ones that simply stick with one kind or another of gummy glue to the fur of passing animals or the feet of birds. In all there are at least 5000 different sorts of migrating birds and bats, by the way, who quickly spread seeds from country to country, often by eating them in fruit, then voiding them next day hundreds of miles away, and later perhaps dying in time to let them germinate in rotting flesh.
Many other seeds have taken to using man to disseminate them, mostly without his permission, some going in for chancy modern tricks like getting picked up in tire treads of cars or airplanes, some stowing away as "weeds" among more popular or ticketed travelers, some just riding unbeknownst in old-fashioned ships, trains, wheelbarrows or shoes. Most remarkable of all from an evolutionary viewpoint may be the increasing numbers who gain willing human cooperation, even to being presented with gay raiment like seed packages that serve as blossoms to catch the eyes of those who may plant them in exotic gardens of unwonted, if not unwarranted, congeniality. A few have even surmounted some sort of pinnacle of spiritual aspiration by becoming the choice of such heroes as young John Chapman of Massachusetts, who in 1806 took two canoeloads of apple seeds down the Ohio River for his now legendary planting tour of the West as "Johnny Appleseed," or merchant seaman Aloysius Mozier who in the 1950s personally handed out more than a million seed packages to needy folk in Asiatic ports.