The Plant World

The smallest bacteria are spheres about a hundred-thousandth of an inch in diameter; the largest trees - the redwoods of California and Oregon - can reach heights of 340 feet.

In terms of size, these are the endpoints of the plant kingdom; and in between fall more than 300,000 known species of bacteria, algae, mosses, fungi, herbs, shrubs, trees, and several other forms of plant life.

Collectively, they form the basis of all life on earth, for no other living thing can survive without them. In addition to producing oxygen, they are the intermediaries that transform the simple elements and compounds of the soil and the air into the complex substances animals need for food. No matter what you eat-with a few exceptions, like salttrace it back far enough along the "food chain" and you come to a plant.

Plants, in fact, have justly been called the food factories of the world. At the same time, although some plants can cause illness, many provide us with a wealth of medicinal substances that help to restore health; and plants supply us, too, with wood, cloth, paper, colour, fragrance, and beauty-to name just a few of their contributions.

Considering our dependence on them, most of us know surprisingly little about plants. This discussion presents some basic facts about them, to provide you with a general frame of reference for a better understanding and appreciation for this part of the site.

The plants of primary interest to us are classified as angiosperms and gymnosperms.

Angiosperms are the flowering plants, a group numbering over 200,000 species. The gymnosperms, represented by only some 500 species, are trees and shrubs, including the conifers.

These two groups account for nearly all the plants considered in this book, the few exceptions being the ferns and seaweeds, club moss, ergot, and Irish moss. The description that follows applies specifically to the flowering plants, but much of it is true of the others, also.

WHAT IS A PLANT?
Look in any dictionary and you will find a more or less involved definition of the word plant. But since no such definition can do justice to the diversity of the plant kingdom, it seems best to avoid that approach here and, proceeding on faith, to describe instead what we don't feel quite competent to define. This may not be the intellectually tidy way, but it's probably more informative.

To begin, then: the parts of a flowering plant are root, stem, leaf, flower, and fruit. Let's consider each in turn.

The Root
Roots are underground parts of plants (but not all underground parts are roots). They have two main functions: 1) they anchor the plant in the ground; 2) they absorb water and minerals from the soil. Many roots, like the carrot, also serve as food storage organs for their plants.

A taproot is a single main root with distinctly smaller branch roots. Fibrous roots are thin and all more or less the same size. The development of the root system depends both on the type of plant and on soil conditions, varying from the use of only a few inches of soil to 50-foot-deep forays in search of water. A single plant with a highly branching root system not untypically develops millions of roots totaling hundreds of miles in length and thousands of square feet in absorbent surface area.

The Stem
Some parts of herbaceous - perennial plants that many people consider roots are actually underground portions of the plant's stem. These are classified as rootstocks (or rhizomes), stolons, corms, and bulbs.

A rootstock grows horizontally in the ground, sending down roots from its lower side and one or more erect stems (or sometimes leaves) from its upper side. One feature that distinguishes it from a true root is the presence of scaly leaves at regular intervals along its length.

The rootstock lives from year to year, sending up new growth each season. Some rootstocks are thick and fleshy; others are long and thin. Some thin rootstocks develop locally thick parts for, food storage; these are called tubers (the potato being the best-known example).

A stolon is much like a rootstock, but it grows along the surface of the ground, sending roots down and stems up at intervals. A runner, like that of the strawberry plant, is a type of stolon.

A corm is a short, thick, vertical underground stem that survives from one season to the next in a dormant state. The second season it produces one or more aerial stems and also one or more new corms. The new corms store food produced by the growing plant and then go through the next dormant period to produce their own plants and corms the following season. The "bulbs" of gladiolus are actually corms.

Bulbs are different from corms, although the latter are often called bulbs. A bulb consists of a short, erect stem enclosed by fleshy leaves (as in onions) or leaf bases (as in daffodils) that serve to store food between growing seasons. Some bulbs survive for several years; others are replaced by new bulbs each year.

The portion of the plant that everyone recognizes as the ateon is more precisely called the aerial stem. Its main function is to bear leaves, the stem with its leaves being called the shoot.

Herbaceous stems are those that contain no woody tissue; these usually die down at the end of the growing season, unlike their woody counterparts in trees and shrubs.

Erect stems are those that grow more or less upward without special support; vines have stems that hail am the ground or climb by attaching themselves to other plants or objects. In addition to bearing leaves, the aerial stem performs the vital functions of transporting water and minerals up from the roots to the leaves and transporting manufactured food substances as they are distributed to all parts of the plant for use or storage.

The Leaf
Leaves come in all sizes and shapes (including some that look more like stems or like flowers), but the typical leafhas a flat blade and a stalk, or petiole, by which it is attached to the stem. Some leaves manage nicely without a petiole; these are called sessile.

Leaves tend to grow in regular patterns on the stem; opposite leaves grow in pairs from opposite sides at the same point along the stem; alternate leaves grow on opposite sides but at different points on the stem; whorled leaves grow in groups of three or more around the stem at one point. Radical leaves grow directly from a non-aerial stem. Simple leaves have a onepiece blade; compound leaves consist of individual leaflets which grow either from a single point (palmate leaf) or oppositely along the leaf stalk (pinnate leaf).

See *** and the definitions in the glossary of botanical terms for explanations of the various shapes and forms-of leaves.

The primary function of the average green leaf is to carry on photosynthesis - the process by which plants use the energy of, sunlight to combine simple substances absorbed from the soil and the air into complex food substances. In the process, plants use up carbon dioxide from the air and produce oxygen.

At night the balance reverses, and plants use up oxygen just as we do; but overall the amount of oxygen produced is greater than that consumed (fortunately for us). The critical agent in photosynthesis is the green pigment chlorophyll: only green plant parts are photosynthetic. Green leaves contain various other pigments as well, but these show up only when the leaf dies and its chlorophyll breaks down.

The yellow and red autumn colours of many trees are due to leaf pigments which are present but are masked by the chlorophyll while the leaves are alive.

The Flower
Perhaps when you read earlier that the function of the stem is to bear leaves, you thought, "What about the flowers?" True enough, the stem does bear flowers, but botanically flowers are merely specialized shoots-specialized for reproduction. The typical flower consists of several whorls (circular ranks) of parts set on a receptacle, the somewhat enlarged end of a stem or flower stalk.

The outermost whorl is the calyx, a set of leaf-like parts (sepals) that protect the flower before it opens. The next whorl in is the corolla, consisting of modified, usually white or brightly coloured leaves called petals. One or more whorls of club-shaped stamens come next; these are the male organs that provide the fertilizing pollen.

The center of all this attention is the female organ, the pistil, consisting of one or more carpels. A carpel is made up of a bulbous ovary which contains the seeds-to-be (ovules), and a stalk (the style), part of which (the stigma) is rough or sticky to capture pollen for fertilization.

Flowers that have the complete set of parts - sepals, petals, stamens, and one or more pistils - are complete; those that are missing one or more parts are incomplete. Perfect flowers have both stamens and pistils; imperfect flowers have only one or the other (a few have neither), being staminate (male) if they have stamens, pistillate (female) if they have pistils.

Some plants bear both staminate and pistillate flowers on the same plant; others have the two kinds on different plants. The tranfer of pollen from stamen to pistil - the pollination necessary for seed to form - is accomplished in various ways, depending on the plant and physical circumstances. The usual ways are by direct contact between stamen and stigma, by insects, or by wind.

Flowers can occur alone or in various kinds of clusters (inflorescences). See the illustration and the definitions in the glossary of botanical terms for details.

The Fruit
In botany, fruit has a much broader and yet more definite meaning than in popular usage: it is the ripened ovary or ovaries-sometimes with associated other parts-of a flower or flower cluster. True or simple fruits develop from ovaries only; accessory fruits (like strawberries or rose hips) develop from ovaries and one or more other parts of the flower. With few exceptions-seedless grapes and pineapples, for example-a fruit forms only after pollination.

Botanically, nuts, beans, corn grains, tomatoes, and dandelion "seeds" are just as much fruits as are blueberries, oranges, cherries, and peaches. You may be surprised to find, though, that tomatoes, cucumbers, and oranges are berries; walnuts and almonds are drupes like cherries and peaches; and peanuts are legumes like peas and beans. Fascinating though it is, a full explanation of the various types of fruit would require greater detail than is possible
here; the glossary of botanical terms contains basic definitions for most of them.

The basic function of fruit is to provide for the dispersal of seed at the proper time, but the fruit also serves to protect the seeds as they mature. Considering that seeds range in size from barely visible (orchid) to over a foot in diameter (double coconut), you should not be surprised to find considerable variety in the dispersal mechanisms that different plants have developed.

Some fruits split open spontaneously while still on the plant to scatter seeds onto the ground or into the wind; others drop from the plant intact but have wings or feathered tufts attached to help them ride the wind. And some maverick plants-collectively called tumbleweeds-abandon themselves to the wind entirely and scatter seeds as they roll along the ground. Some seeds are spread mainly by birds and other animals, which eat the fruit but excrete the undigested seeds.

Prickly fruits often hitch a ride on passing animals or-people who carry them elsewhere; others can. float on water until they are washed up on a new shoreline. There 'are still other ways, but these are enough to suggest the boundless ingenuity of Nature in providing for the propagation of each species. -

THE NAMES OF PLANTS
If botanists had to rely on the common names of plants in their work, they would spend most of their time trying to figure out which plant was meant by Ia given name. One man's redroot would be another mans green amaranth, and which of many plants was meant by healall would be anybody's guess. The problem would be compounded when botanists speaking different languages tried to communicate, or when one of the many plants without common names was being considered.

The binomial system, using a pair of Latin or latinized words to identify each species, solves the problem by providing a nearly unambiguous way to name plants (and animals too), independent of popular names and language differences. The first and second parts of the binomial, or botanical name, identify the genus and species of the plant, the species being, the smallest group that can be consistently identified as distinct from other groups.

The genus includes various species that show certain common elements. There are further levels of classification above genus, but these need not concern us here.

The genus name is always capitalized; the species name is usually not capitalized but may be (optionally) for some plants. The two names are usually derived from an historical name for the plant, a physical characteristic, a use to which the plant has been put, a geographical location, or the name of a botanist being honored. Some examples:

Common Name	Genus	Species
Dandelion	Taraxacum (from an Arabian name for the plant)	oflicinale (medicinal)
Houseleek	Sempervivum (Latin for "live forever")	tectorum (pertaining to houses or roofs)
Ginseng	Panax (from the Greek root of "panacea")	quinquefolius (five-leaved)
Lobelia	Lobelia (after the botanist de Lobel)	inflata (swollen, referring to the calyx)

There are some species that include plants with significant enough variations to be categorized. These are accommodated by adding another term to the binomial; for example, a particular variety or subspecies of sweet fern (a shrub rather than a real fern) is designated Comptonia peregrina var. asplenifolia (or just Comptonia peregrine asplenifolia) because its leaves resemble the fronds of asplenium ferns.

Even the binomial system is not foolproof, however. Authorities sometimes disagree on the relationships among plants, so that several botanical names can become attached to one plant.

To handle this problem without having to resolve it, botanists generally add to the botanical name they use an abbreviation of its author's name. Thus, Bellis perennis L. indicates that Linnaeus, the Swedish botanist and naturalist who originated the binomial system, assigned this binomial to the wild daisy.