by Guy Murchie
by big, spiral-shaped protein molecules called enzymes or catalysts, which seem specially prepared to handle it and promptly introduce it to freshly inhaled carbon dioxide (likewise in the hands of specialized enzymes) in such a way that the two substances immediately go into a kind of dance called a chemical cycle in which ingredients are intermittently added and extracted as they whirl and merge into new wood. To this I'll only add, at risk of whimsy, that the chlorophyll molecule's daisy shape is beautifully appropriate because the word "daisy" derives from "day's eye," meaning the sun, who not only energizes all vegetal growth (through chlorophyll) but is reflected in every sun-shaped daisy with the golden orb and white rays you see nodding in the meadow.
Of course photosynthesis is really very much more complicated than my brief portrayal suggests, because it also includes all sorts of less obvious molecules, such as carotenoids that help chlorophyll absorb energy of out-of-reach frequencies, other varieties of chlorophyll, various salts, minerals and trace elements from the soil, whole retinues of burly catalysts (such as ferredoxin, adenosine triphosphate, etc.), subcatalysts, acceptors, bouncers, cops, cooks, nurses, janitors and other chemical functionaries who keep things coming, going, stewing, growing - and literally bookfuls more ...
When you think that all this is going on naturally and invisibly amid intricate valves and thermostats and regulators as if in a vast automatic factory inside every fluttering leaf, it is truly appalling - and you can hardly grasp the immensity by reminding yourself that the millions of invisible subcell chloroplasts in a leaf are huge football-shaped worlds in relation to the bustling industry within, each chloroplast packed with thousands of coin-shaped grana in neat piles, each granum in turn bristling with tens of thousands of bead-shaped quantasomes, each quantasome made up of about 200 daisy chlorophyll molecules, each of whose 137 atoms contains the mystery of creation!
TRUNKS
Although we mentioned the vegetable's need for water in discussing roots and leaves, we must come back to water again now in order to describe how stems or trunks work. But this time the subject is not just finding water in the soil or later transpiring it into the air: it's the in-between problem of raising it as sap from many feet underground all the way up to the highest foliage - something that would seem a formidable feat in the case of a measured 368-foot giant redwood, which, counting its roots, could add up to a total height exceeding 400 feet. For, as water cannot be lifted more than 33 feet by earthly atmospheric pressure (which, believe it or not, is the force that "sucks" a drink up through a straw), something a lot stronger must be responsible. That something, according to a recent postulation, could be the pumping action of submicroscopic filaments that work like cilia. But the general consensus of botanists points first to the vertical pressure differential inside the tree, a force sometimes exceeding a quarter of a ton per square inch, though normally averaging closer to 350 pounds. In early spring it pushes the sap water up the tree, mainly with pressure generated from below by root osmosis (osmosis being the tendency for a permeable membrane to pass more liquid in one direction than the other), but as soon as the leaves sprout and begin chemically to consume as well as evaporate the upper moisture, the negative pressure thus created in them pulls (by molecular tension) the tiny columns of sap all the way up from the roots and at speeds that sometimes exceed two thirds of an inch a second. This is possible because the chemical action (photosynthesis) in the leaf is immensely powerful and the hydrogen bonds in pure water (H2O) give it great tensile strength (up to about 2 1/2 tons per square inch). Moreover it has been dramatically demonstrated through several kinds of tests on trees that in summer not only does the sap start rising every morning in the twigs earlier than in the bigger, lower branches, which in turn precede the main trunk and roots, but also tree trunks actually shrink to a measurable degree on hot days (due to the negative pressure within them) and, if punctured with a small hole, can be heard to hiss as they suck air inward.
If sap flow toward the leaves is hard to explain, the oozing of leaf gruel away from them is harder, roughly in proportion to its slowness, which takes minutes instead of seconds for each inch of advance. Some botanists say the gruel must be pushed by its production in the leaves because, unlike sap, it maintains a positive pressure in the growing season. But a few surmise there may be some sort of a physiological pumping action in the tiny bast tubes which, they suggest, may have already begun to evolve into organs that will ultimately be describable as rudimentary hearts.
GROWTH
The first pioneer experimenter in botany to come to such a bold hypothesis, so far as I know, was Sir Jagadis Chandre Bose, founder and director of Bose Research Institute in Calcutta, who wrote about it in his Plant Autographs and Their Revelations in 1927, after inventing and developing the crescograph, an extremely delicate growth-recording instrument that revealed faint "peristaltic waves" in stems and tree trunks which increased whenever it rained and diminished during droughts. The telegraph plant (Desmodium gyrans), he particularly noted, has a kind of slow pulse and every three minutes its leaves nod slightly downward then gradually rise again. Whether such a rhythm, perceptible in some degree in many plants, may signal the beginning of evolution from the vegetable to the animal is a question only future research can decide.
Meantime we should not presume that plants, embedded as they normally are in all the nourishment they need, have neither motive nor capacity to move about. For move they certainly do, and some get around actually faster than some animals, particularly such sedentary animals as barnacles, sponges and coral. A good example of a traveling vegetable is the slime mold that creeps and swarms over rotting stumps like an army of amebas. And there are the microscopic diatoms found swimming in all lakes and seas, who propel themselves with jets of protoplasm, (im) some of which flow along slits in their sides, something like the paddles of sidewheel steamers. Also algae and ferns have spores or sperms that swim with whiptails, and a few species of these vegetable microbes attain a speed of more than half an inch a minute which, in proportion to their size, is impressive. If you compare a human sprinter running 7 times his height in a second with a jet airplane flying 50 times its length in the same period (at twice the speed of sound), the zoospore of a mere vegetable (aptly called Actinoplanes) has beat them both at an astonishing 100 times its own length in the same brief interval!
We will later consider some of a vegetable's other kinds of motion, such as opening its blossoms to the warmth of day, turning to face the sun, growing upright from a random seed, twining around a support, catching a fly, dodging a cow... but now let us behold in wonder the simplest motion of all: ordinary growth, which, in a plant, is required for just staying alive. According to Bose's high magnification crescograph, which automatically records a plant's growth on a graph on smoked glass, the average plant in India grows about one one-hundred-thousandth of an inch per second (almost an inch a day) with a slow pulsing motion, each surge upward followed by a slower recoil of about a quarter of the gain and the steps in the graph getting steeper and wavier at times of rapid sprouting, leveling out during drought and becoming completely horizontal at death.
Certain plants, however, "grow" much faster than the average, the fastest of all being probably bamboo. Indeed I saw a report in 1970 of a stem of madake bamboo that had grown a measured 47.6 inches in 24 hours. That is as fast as the minute hand of a watch and considerably faster than an ameba (a free animal) can move in any direction.
In Burma, during World War II, I recall that there were a number of occasions when soldiers by heroic efforts chopped a road through the jungle only to discover too late that they could not return over the same route a week after it was "finished" because of the tremendous volume and stubbornness of new shoots that had sprouted there as soon as the cutting stopped. I particularly remember hearing of an army truck, parked beside the road on a Tuesday morning during the monsoon, which would not budge the following Friday night because, as the sergeant driver explained, it
had been "bamboozled" by the 3 1/2 days' growth of bamboo that literally staked and wove its wheels and axles to the ground. If one could consider the kingdoms of nature to have been participating in the war in Burma, one would have to concede that it was the vegetables that generally emerged victorious over the humans and their mineral slaves.
Yet growth in such a plant as bamboo (really a genus of grass with exceptionally large elongation zones) is accomplished not so much by cell division as by mechanical swelling of cells. Indeed bamboo practically drinks its way upward, continuously extending its vertical pipelines by means of material they themselves have lifted. This lifting of course is accomplished through the pressure and friction of water in motion, for water is not just a drink, as any sailor can tell you, but at least as much a medium of transport - in vegetables even more than in animals, both kingdoms attesting thus to their evolutionary beginnings in the sea. In the cells of grasses and flowers, furthermore, water provides the vital pressure that gives them the stiffness to stand erect, without which they must immediately go limp or, in flower language, wilt. One can hardly be reminded too often indeed that water literally permeates all life on Earth, not only flowing daily through your body (of which it amounts to some 60 percent) but even more continuously through all vegetables (where it averages nearly 75 percent). And, besides water, there is the mysterious synthesis of vital substances from each of the three kingdoms of which vegetables are made - a synthesis that implements and coordinates everything from limb orientation to the processions of root hairs through Earth that resemble sheep grazing progressively farther and farther down a green valley, the complexity of their orderly interchange of materials being of the very essence of life.
This underground commerce furthermore accounts in large part for the basic order in any sort of vegetal growth. It hints at why baby plants first sprouting from seeds lose weight (like most babies at birth) for several days before they become adapted to their new freedom and, breaking the surface of the ground, gain the carbon dioxide and sunlight they need to photosynthesize their food and start increasing their total mass. It tells why something similar happens with transplanted saplings, which, like new kids in school, are awkward for a while as their roots and branches adjust to unfamiliar grounds and companions.
At first the sprouted seed, even while losing weight, multiplies the number of its cells at what a banker would call a compound interest rate with principal constantly increasing: the cells dividing and the new cell (though smaller) dividing again and again, virtually doubling their number at each generation. But as soon as the organism is mature enough to develop specialized zones in roots and shoots, its cell multiplication slows down toward a simple interest rate with fixed principal: new cells produced by the meristem zones elongating but (by then no longer meristem) not dividing again.
FORMS
Each kind of plant of course has its own genetic character and attains its maximum growth rate according to its magnitude and capacity, the lupine at about ten days of age, the cornstalk in its sixth week, the beech tree after a quarter-century. And each one sprouts branches at angles and intervals of its own pattern, by which it may be recognized as a particular kind of tree or bush or flower from as far away as it can be seen. This basic order in branches is obscured, to be sure, by their more apparent randomness, yet the most careful measurements have confirmed that small nodes of meristem are methodically left behind the main meristem zones as they advance, and it is these nodes that later develop into knots and branches whose characteristic arrangement labels them as elm or oak, jasmine or jonquil in a subtle and beautiful harmonic periodicity. There is time as well as space in this vernal music too, for branches are born on different days as well as in different positions as surely as tree-ring calendars show both years and girths.
To be explicit, one of the simplest tree forms (found in maples, ashes, horse chestnuts and dogwoods) is the pairing of leaves, twigs or branches, two of which grow out from their mother stem exactly opposite each other, while the next pair (above or below) also grow opposite each other but at right angles to the first pair, giving maximum dispersion of foliage. A slightly more complicated form found in many more trees is the spiral. To see it clearly, tie a string to the base of a leaf, then extend the string along the twig and branch, looping it once around each leaf stem you come to, in as smooth a curve as possible. In the case of an elm or linden you will find the average leaf tends to be attached just halfway (180°) around its twig from the next leaf, so the string will spiral tightly at the rate of 1/2 turn per leaf. A beech tree, having leaves at only 120° intervals, yields a rate of 1/2 turn per leaf. An apple tree, oak or cypress with the common distribution of leaves at 144°averages 2/5 turn, a holly or spruce 3/8, a larch 5/13 is, and so on. If you are mathematically inclined you may have suspected
by now that these fractions are not just random, for in fact each numerator and each denominator is the sum of the two immediately preceding it, both sequences of numbers forming the same simple and regular progression: 1,1,2,3,5,8,13,21,34,55,89,144,233,377 ... This particular sequence was long ago named the Fibonacci series because a man by that name investigated it in Pisa in the thirteenth century. And it turns out to be the key to understanding how nature designs trees and is presumably a part of the same ubiquitous music of the spheres that builds harmony into atoms, molecules, crystals, shells, suns and galaxies and makes the universe sing.
Obviously in the vegetable kingdom it is not limited to the branching of trees. Its fractions beyond 3/8 have frequently been found in plants with compact seed or leaf systems, such as mosses, cabbages, or the florets in the center of petaled flowers with spirals going in both directions. Five thirteenths includes the white pine cone in which 5 turns of a spiral produce exactly 13 of its scales or seeds. Daisy centers use the three consecutive fractions 13/34, 21/55 and 34/89 and at least one sunflower head (22 inches in diameter) was recorded at Oxford University at an impressive 144/377 or 377 seeds to a spiral of precisely 144 turns!
If you suspect these are freak cases and that nature really has quite a carefree attitude toward mathematics, just try telling a pine tree to grow some way it doesn't want to. I mean, tie the tips of its branches so that the tall central one, the leader is bent away from its accustomed verticality or the surrounding ones (in the case of a young white pine) from their stubborn 70°angles outward. No matter how you fix them, they will insist on growing back at their accustomed angles wherever and whenever they can reach, writhe or burst out of their bonds, for their geometric character is built into their very life. That is the abstraction that distinguishes one kind from another and it is geometric not only in the original Greek sense of basing its measurements on the earth (mostly through gravitation) but also on the earth's ancestors, the sun and to some extent the stars (through light and less obvious kinds of radiation), all of which give plants in general (as well as most animals) their bearings.
And the spirality of plants, when they have it, gives them the further identification of handedness, right or left, which may also (through molecules or inertia) be geared to the planet. At any rate the skewed tree or flower is most apt to turn clockwise going away from the observer (like a common corkscrew), which is called right-handed, to distinguish it from the less common left-handed or counterclockwise motion. This is particularly noticeable in helical climbing vines, some nine tenths of which, like seashells, are right-turning, as are the molecules of protein in all earthly flesh. Thus bindweed goes right with the majority, while honeysuckle twines left with the wayward few, a disparity that may have been at the bottom of Ben Jonson's observation in 1617 that "the blue bindweed doth itself enfold with honeysuckle" in a passionate embrace that to this day has never ceased to fascinate poets and geometricians.
If the turning of the earth were the direct or primary cause of the handedness of its vegetables, of course one would expect a variety that spirals clockwise north of the equator to turn counterclockwise when south of it, where the so-
called Coriolis or torque effect is opposite. But so far there is sparse evidence that the equator is a definitive boundary between right and left vines, trees, shells or other creatures. Nevertheless, physical forces do definitely influence growth. Not only do mechanical tensions (presumably induced by hydraulic pressures) in their tissues keep grass and flower stems stiff enough to stand up in the wind (proven by the way stalks curl outward when cut and split in two) but, like animal muscles, plant fibers grow with exercise. D'Arcy Thompson reports an experiment in which several young sunflower shoots of a size that had broken in tests when loaded with 160 grams were left for two days bowed down by oppressive weights of 150 grams, after which ordeal they were individually strong enough to carry 250 grams. Then, in less than a week of further training, they developed so much stamina that each shoot could easily heft more than 400 grams!
Perhaps this is mostly a mechanical process of forcing fibers to line up parallel to the components of tension applied to them, as is known to happen with the chain molecules in molasses (a liquid vegetable) when it is boiled to a plastic solid and drawn into a rope of taffy, which can be continuously folded, twisted and pulled until the housewife finds it too tough to stretch any farther. If so, is form then created by the molecules that compose it? Or are the molecules rather produced by the form and function of the whole? Such philosophical questions come up again and again in the study of life and we will delve into them later on in this book. Here there is room only to make a preliminary inquiry into the cause and effect of growth which can but suggest a few macrocosmic factors that seem to influence what any particular plant is to be.