MOST of the plants in our fields and gardens usually are grown from true seeds. Many other plants must be propagated in another way.

To do that, we cut small sections of living stem or root tissue from the parent plant. We handle the cut sections in one of several hundred different ways. In due time we have new plants exactly like the original ones. This seedless method of increasing plants is asexual, or vegetative, propagation, which is essentially the development of entire plants from buds.

Plants so grown are literally and actually "chips off the old block." They therefore have the qualities of the original plant.

We use vegetative propagation for two basic reasons.

First, some plants do not commonly produce seeds and hence must be propagated vegetatively. The seedless grape is one example. Another is garlic. No one in this country has ever produced true seed of garlic, although its near relative, the common onion, almost always is grown from seed. Other plants that produce flowers but seldom, if ever, a seed are horseradish, pineapple, some palms, sugarcane, some bamboos, bananas, and certain sterile hybrid plants. Still other plants, such as the common ground-ivy (Hedera helix), rarely produce flowers. Vegetative propagation is the most economical way to increase them.

The second reason is that many seed-bearing plants do not breed true—that is, seedlings that grow from their seeds do not closely resemble the parents. We could plant seeds of the Delicious apple, or Peace rose, or Meyer zoysia grass, and get seedlings that definitely are apples, roses, and zoysia grasses, but we would lose the identifying characteristics that made the originals famous. In short, when we buy new plants of the Delicious apple or another named variety, we want them to be identical with the parent plants and with each other to the extent that we can distinguish no differences in them.

Our sole purpose in propagating named varieties of many plants—woody ornamentals, tree fruits, small fruits, grasses, ornamental perennials, white potatoes, sweetpotatoes, bulbs—is to keep intact the variety features that we prize.

Valuable breeding stocks of alfalfa and other field crops often are maintained vegetatively to insure the exact genetic makeup in the resulting seed and thus prevent the unavoidable change that occurs when they are increased by true seeds.

We choose and plant named varieties of certain plants in our fields, gardens, and orchards primarily because we know they have certain desirable features, but the only way we can be reasonably certain of getting plants absolutely true to variety name is by propagation of stem or root tissues of the original parent plant.

VEGETATIVE PROPAGATION has its limitations.

For the same reason that it is a highly desirable means of maintaining the status quo in a variety, the usefulness of vegetative propagation is restricted to this purpose, and consequently it cannot be used to develop new varieties of plants. It is always necessary to resort to sexual reproduction in order to obtain true seed with which to develop new varieties of crops that commonly are propagated vegetatively.

To create a new variety of white potato, for example, we must allow the potato plant to grow, form flowers, pollinate the flowers, and then allow the seedballs to develop. Occasionally when weather conditions are suitable and the seedballs are formed naturally, the event is so unusual that many gardeners are bewildered to see "small tomatoes" growing on their potato vines.

Improvement of plants that normally are propagated vegetatively by pollination and formation of true seed is exceedingly slow. For white potatoes, about 1 million seedling plants must be grown in order to obtain one selection worthy of being named as a new variety. From that point onward, it must be maintained vegetatively.

New forms or varieties of plants can appear naturally—but very rarely! —in vegetatively propagated plants as the result of sports. Another name for sports is mutations. Sports and mutations are plants or parts of a plant that abruptly show a noticeably different appearance from the rest of the plant.

Such a change, if it is the result of a true mutation, may be maintained by vegatative means once it has occurred.

Examples of changes in a sport or mutation are a deeper red in a red apple, an unusual color or shape in a flower, a different leaf color in a shade tree, double flowers instead of singles, and similar noticeable changes.

For some unknown reason, mutations, which, as we said, are rare in most plants, occur so often in some sweetpotatoes that it is difficult to maintain a variety unchanged even by vegetative propagation.

WHEN WE increase plants by vegetative reproduction, our aim is to stimulate the growth of buds on "borrowed" roots and stems or to encourage the formation of entirely new buds and roots from primordial—first-formed—tissue.

There are essentially two types of buds of importance in vegetative propagation—true and adventitious buds.

A true bud is a growing point that usually is formed at the base of a leaf and along the stem of a plant.

True buds occasionally may remain inactive and are made active only by some unusual stimulus. For example, an apple tree, if cut, may grow new shoots from the stump when the inactive true buds are stimulated to grow.

True buds may develop into leaves, flowers, or stems. Inactive true buds are "reserves" and function only when active true buds are killed or removed or do not grow for some other reason.

Adventitious buds are formed from embryonic or undifferentiated tissue cells in the roots, stems, or leaves. Given the proper stimulus, these cells form buds that in turn may form either roots or sprouts, depending on their location.

Theoretically, any living cell in the plant may be stimulated to form a bud and ultimately a new plant. In fact, fully developed carrot plants have been grown experimentally from a single root cell of a carrot.

Such development, however, usually is easiest from the cambium (a soft formative tissue just under the outer bark, which is the growing layer in most stems); the pericycle (undifferentiated cells surrounding the central cylinder); or rarely from phloem tissue (the tissue in which food materials are transported within the plant).

Adventitious buds in a sense are emergency buds, which insure the perpetuation of the plant when it is in danger of dying for lack of true buds.

The structure of the plant largely determines the method of vegetative propagation that we can use. Thus in propagating plants classified as monocots—pineapple, sugarcane, and bamboo, for example—it is difficult or impossible to stimulate adventitious buds. We achieve vegetative increase by stem tillers or offshoots or from inactive or latent buds at the nodes of the stems.

In the plants classified as dicots, bud formation is not so restricted because the cambial and other undifferentiated tissues are distributed more widely. It is rather easy therefore to stimulate the growth of adventitious buds in most dicotyledonous plants.

True stems are used oftenest in asexual propagation methods. They include cuttings, grafting, and budding. Other modified stems are used—tubers, stolons, rhizomes, tillers, bulbs, and corms.

Stems differ from true roots in certain basic ways. We all know that roots always grow down toward the center of the earth, but stems, even though they are underground tend to grow upward. The distinction between roots and stems that is of greatest importance in vegetative propagation is that stem buds are formed on the surface while roots have no surface buds.

Bud growth from roots is adventitious and is always initiated from the internal tissue.

VEGETATIVE PROPAGATION may be applied to both underground and aboveground parts.

Belowground parts would include roots, tubers, stolons, rhizomes, tillers, bulbs, corms, and mycelium. (Mycelium is the threadlike vegetative growth of fungi that develops underground more or less as roots do for most plants. In mushrooms mycelium is commonly called spawn.)

Aboveground parts involve stems for cuttings, layering, grafting, and budding.

Plants often are increased directly from true roots by two primary methods, root suckers and cuttings of whole roots.

A true root sucker is formed when an adventitious bud develops from the internal root tissue and continues growing into a stem. Root suckers are sometimes produced naturally near the base of the parent plant and form dense, close-knit clumps, which easily can be lifted and separated.

In plants like the raspberry, the root suckers occur at some distance from the parent plant, and we get new plants merely by cutting the connecting roots.

Two variations of the usual root-cutting method are used commercially—induced suckering and undisturbed whole-root cutting.

Induced suckering is useful in species that rarely produce root suckers. By this method, suckers form in response to partial girdling or cutting of an exposed root in such a way that the partly severed root receives some nutrients from the parent plant.

Undisturbed whole-root cutting merely goes one step further. The exposed root is severed completely, and the cutoff portion is left in the soil.

Polyethylene plastic film has recently come into common use for rapid rooting of softwood and hardwood cuttings. Methods employed are simple.

Cuttings are prepared in the usual way in lengths of 2 to 6 inches, depending on the material to be propagated. The stem is cut off at an angle of 45 degrees just below a node. One-half to one-third of the lower leaves are removed. Unusually large leaves are cut back to one-half their length to save space and reduce loss of moisture.

Cuttings must be kept fresh and turgid from the time they are removed from the plant until they are placed in the rooting medium. Freshness may be preserved by placing cuttings in a polyethylene bag or between layers of damp paper or cloth. Cuttings root more quickly if they are treated with a rooting compound—such as Hormodin #2 or #3—before they are inserted in the rooting media.

Single cuttings may be rooted by placing a small amount of damp sphagnum moss in a square piece of plastic. The cutting is inserted in the moss, and the plastic film is pulled up around the stem and tied. The bundle is then placed in a situation where there is good light, such as a window sill or screened porch.

Under favorable conditions, rooting should be accomplished in 2 to 5 weeks, depending on the species. Such house plants as African-violets, gardenia, begonia, coleus, and peperomia may be handled in this way with little care and space.

In rooting larger numbers of cuttings with the aid of plastic film, a moist medium of equal parts of sand and peat gives good results. The mixture is placed in clay pots or shallow wooden trays or packed in plastic bags. After cuttings have been inserted in the medium, the tops of bags are closed and held tightly with rubber bands. Clay pots are enclosed in polyethylene film held tightly by rubber bands. Flats are sealed by tucking the plastic under the base of the flat. If tall cuttings are being rooted, the plastic canopy may be held above the cuttings by a light frame of wire or wood.

A technique of rooting cuttings under a fine mist has been developed. It is particularly for commercial propagators, but adaptations are of interest to home gardeners.

Four conditions are necessary to operate a mist system successfully: An adequate supply of fresh water under pressure; perfect drainage of the rooting medium within the propagating bed; proper types of nozzles; and propagating beds or frames, 3 to 4 feet wide, constructed of wood, concrete blocks, or brick.

The length of bed depends on the size of the operation. Ordinarily one nozzle will cover an area of 10 square feet. Nozzles may be placed 3 to 4 feet apart in the center of the bed. Usually they are mounted 12 to 16 inches above the bed. If the mist is to be intermittent rather than continuous, there must be electric controls and timing devices.

Under mist systems, cuttings root best in porous mediums, such as sand and peat, vermiculite, perlite, and clean sand. Drainage is provided by 2 to 3 inches of coarse gravel placed under the rooting mediums. Water may be supplied from pipes above the bed or brought up through the bed from pipes inside or below the bed. Types of nozzles in use vary in capacity and design. Under most conditions a discharge capacity of 1 or 2 gallons of water an hour gives good results.

Home gardeners may wish to operate a simple mist system out-of-doors during the summer. One or two nozzles connected to a hose may be operated manually during daylight hours to provide good rooting conditions. The bed should be protected with a plastic shield around the sides. The shield should be of sufficient height (about 18 inches) to contain most of the mist within the enclosure. A hinged plastic cover may be provided to fit over the top of the frame. It is necessary to provide ventilation on warm days by raising the cover a few inches and opening one side or end of the plastic shield. Cuttings for mist propagation are prepared in the same way as are those to be rooted in plastic-enclosed pots or wooden trays.

Plants may be air layered by cutting a deep gash into the stem, wrapping the wound with moist sphagnum moss, and then covering them with polyethylene plastic to keep the moisture in. This method is successful for plants that are hard to root by other methods.

THE SWEETPOTATO, a true root, is propagated mostly by root suckering.

Sound, medium-sized roots are laid on a loose bed and covered with an inch or two of sand or sandy loam. Sometimes the roots are cut lengthwise; the cut surface is treated with a fungicide to prevent rot and placed downward, so that the plant-producing surface is uppermost.

The young root suckers, 3 to 5 inches high, are pulled off in 4 or 5 weeks, and others emerge to take their places. Three or four crops of sprouts may be obtained from each "mother" root. The sprouts are true root suckers in that they originated from adventitious buds in internal tissue of the roots.

Sweetpotatoes also root readily from stem cuttings, a method that we discuss later.

Whole-root cuttings, by which new plants can be produced from short pieces of root, are used more commonly than root suckers.

With root cuttings, an adventitious bud may be initiated from callus tissue at the proximal end of the root (root end nearest the parent plant); or from tissue near the proximal end of the plant (as in horseradish); or from tissue anywhere along the root (raspberry).

The root cutting furnishes all nourishment to the young plant until it becomes self-sufficient. The original root cutting often becomes a part of the new plant, but it may also function solely as a source of nourishment.

One should mark the tops and bottoms of root cuttings to avoid planting them upside down. Horseradish roots when inverted (that is, when the proximal end—the end that normally was the stem end—is planted downward) will grow and develop stems from the proximal end and roots from the other end. Growth is retarded, though, and the resulting roots are small and unsalable. Growers who make root cuttings therefore cut the upper (proximal) end square and the lower (distal) end oblique. Root cuttings thus marked can be properly placed when they are planted in the field.

Curly aspen, a forest tree whose wood is valued as a veneer for furniture, must be reproduced vegetatively or the wood will be similar to that of ordinary aspen.

Shipmast locust grows fast and is straight, but it must be propagated from root cuttings in order to retain those special qualities. In fact, it seldom produces viable seed.

Smilax, oriental poppy, halesia, amelanchier (shadbush), and shepherdia are examples of plants often propagated by root cuttings.

Some root tissues do not commonly form adventitious buds. Dahlias and peonies, for example, have large, fleshy storage roots, which will not grow unless a bud from true stem tissue is attached. Such propagations are not true root cuttings, but, strictly speaking, are stem cuttings with attached nonregenerative storage roots.

ALTHOUGH the storage organ of the white potato is formed underground, it is really stem tissue, because it has true buds (eyes), which grow from the surface layers.

The eyes of white potato are formed only during the early stages of growth in much the same way as buds form along the stem of a woody plant. If the eyes are removed mechanically, the tuber usually will not grow. (The sweetpotato a root, produces adventitious buds after the root is fully grown.) Consequently, when plants are propagated by cuttings from a tuber, care must be taken to include at least one eye or bud on each seedpiece.

Tubers are used to propagate white potatoes and Jerusalem-artichokes. Blocky seedpieces weighing 1.5 to 2 ounces and having two eyes or more are desirable. These may be cut and planted immediately, but if the soil is overly dry or wet, they may first be healed. The process of healing of the cut surface of a potato is called suberization. Suberization occurs in about 7 to 10 days at 60° to 70° F. and a relative humidity of about 85 percent.

Potato seed that has been precut at the farm where it was grown is suberized during transit in railroad cars equipped to provide suitable temperature and moisture. The seed arrives at its destination ready to be planted.

Sometimes potato "eyes" are marketed for seed. They really are small seedpieces, cut to include the eye and a small part of the storage tissue. Because seedpiece eyes weigh little, they are desirable for a special garden trade. They are usually cut and packed in fine sawdust or similar material for suberization and subsequent mailing. Eyes are not recommended for the commercial production of potatoes.

The tubers of other tuberous plants, including gloxinias and tuberous begonias, may be cut before planting (again with an eye in each piece), but they usually are planted whole.

STOLONS, rhizomes, and tillers are stem structures that frequently grow under or near the ground surface in more or less specialized patterns.

Usually we call it a rhizome if the stem tissue remains partly underground and occasionally sends up leafy shoots from the upper surface and roots from the lower surface. Examples are the German iris and canna.

The crown roots of asparagus and lily-of-the-valley usually are considered to be rhizomcs. Usually they are semi-fleshy, thickened storage stems, unlike stolons or runners, which are usually slender, aboveground stems that most frequently take root at or near the tip.

Most persons are familiar with the stolons, or runners, of strawberries, which represent the commonest means of propagating this important crop. Stolons also are utilized to increase named varieties of many important lawn grasses, including St. Augustine, zoysia, bermuda, and bent grasses.

Somewhat distinct are tillers, or offsets. They are stem sprouts that usually come from the underground axils of the lower leaves. In general, tillers arise at the base of the parent plant and form a cluster or clump of plants.

Tillers represent the only means of propagation for certain monocots, which, because of their lack of a continuous cambium layer, cannot be budded, grafted, or grown from cuttings. The date palm, which does not breed true from seed, for example, can be propagated only by tillers that develop near the base of the parent.

Propagation of new plants by means of rhizomes, stolons, and tillers is probably the most easily accomplished of all the methods of asexual propagation. One need only transplant the rooted plants, which are readily separated from the parent plant. Commercial nurserymen find this method relatively slow and cumbersome.

A BULB is a thickened fleshy bud. Usually it grows underground. It has specialized storage parts, which provide a convenient means of vegetative propagation. The onion, lily, hyacinth, tulip, and narcissus are known as bulbous plants.

If there are continuous rings of scales around a central growing point or axis (as in the onion, tulip, hyacinth, and narcissus), the bulb is known as a tunicated bulb.

Bulbs that have individual scales attached to the axis in a rather loose manner (somewhat like ruffled feathers on a chicken) are known as scaly bulbs. The lily is a scaly bulb.

True bulbs increase by division by breaking up into a number of smaller parts, which, in a few years, develop into a bulb of flowering size. During the time of maturing, bulbs also form offsets, or small bulbils or bulblets, which appear outside of the protective sheath (as tulip and hyacinth).

Some plants form new bulbs every season of growth, as tulips do. Others, like narcissus and hyacinth, grow new tissues around the old bulb to increase in size and later may divide or split into new bulbs. Propagators generally agree that bulbs originating from offsets are more vigorous or thrifty than those formed from divisions.

The planting of bulbs is regulated in part by the size of bulb, seasonal conditions, species, and such other factors as the type and drainage of soil.

Tulips and lilies may remain in the soil year after year, but stronger plants and better blossoms will result from frequent digging, sorting, and resetting of the largest and strongest bulbs. The average gardener is best guided by the planting and cultural directions recommended by the distributor.

THE CORM is not a true bulb but often is called such in commercial trade.

A corm is a thickened underground stem that contains nodes and inter-nodes, as in gladiolus, crocus, and related types.

When it is properly planted in the fall or spring, a corm thickens its leaf blades above the old corm to begin the formation of a new one. Cormlets start to form at the base of the new corm during the flowering period. The old corm becomes detached or decays, and the new corm formed above the old one may be encircled by cormlets, which, if separated and planted, will usually produce flowering-size corms in 2 or 3 years.

Gladiolus corms generally are dug in the fall after the flower stalks have died and are placed in dry storage until planting time the following spring or early summer.

Crocus is usually fall planted and may be left in the soil more than one season. The corms have to be replanted at intervals of 2 or 3 years, however, as new corms formed on top of old ones tend to produce plants that are too shallow for good flowering.

THE MUSHROOM plant grows underground in the form of fine fungus threads, called mycelium. Spawn is made by culturing the mycelium on a solid medium, usually rye-grain. Mushroom growers inoculate their beds by broadcasting pieces of spawn over the surface. The mycelium grows into the beds from each piece of spawn.

Unlike the roots of green plants, however, the growing strands of the many separate "root systems" soon fuse with each other.

Strains of spawn are improved by testing and selecting cultures made from single spores and from strains that develop during mycelial growth. The differences between strains grown from single spores are due to genetic segregation in the mushroom. The growing mycelium is usually rather stable, but new strains sometimes arise spontaneously. Presumably they are due to mutations.

REGENERATION by cuttings is basically a form of bud propagation.

The modern use of rooting compounds, mist systems, plastics, and improved rooting media has increased the range of plants that may be propagated profitably by this means.

A cutting may be made from any part of a plant from the root to the growing tip.

We can list three general classifications of cuttings: Cuttings from stems; cuttings from growing or soft wood or semihardwood; and cuttings from ripened or mature wood.

Growing-wood cuttings may be prepared from soft or hardened wood. The length of cuttings may vary with the length of stem between nodes. Cuttings usually contain two to five buds. The upper end of the stem is cut off on an angle just above the topmost bud, and the lower end is cut off just below a bud. Plants that often are propagated from soft growing tips include coleus, salvia, verbena, geranium and viburnum.

Semihardwood from healthy plants often is used for cuttings. A rule-of-thumb method of testing for proper condition of wood is through a bending test. If the wood snaps readily and does not remain bent and springy, it is considered acceptable for use. Cuttings of this type are usually taken during the summer after the period of flowering. Plants of commercial importance that are propagated from semihardened wood include the azalea, camellia, osmanthus, ligustrum (privet), and lonicera (honeysuckle). Many plants can be propagated from soft or semihardwood cuttings.

Hardwood cuttings are taken from well-ripened, mature stems collected after the leaves have fallen. Many plants of the nursery trade are propagated from cuttings taken in late fall and winter. Among them are the grape, rose, spirea, arbutus, tamarix, and euonymus.

Boxwood, most conifers, and some of the broad-leaved evergreens are rooted successfully from cuttings taken in late December and January.

Whole leaves and leaf sections are used to regenerate some of the house and conservatory plants, such as African-violet, gloxinia, rex begonia, and peperomia.

For plants like gloxinia and peperomia, the entire leaf is used. It is inserted upright in moist sand to the depth of the petiole (leafstalk).

Rex begonia is propagated from leaf sections, each of which has a basal portion of the midrib. The sections are inserted upright in sand. Another way is to sever the main veins and place the entire leaf flat upon the rooting medium.

A complete, mature leaf of the African-violet is removed from the parent plant by cutting it near the crown to avoid leaving a stub. The cutting may be rooted in water, sand, peat moss and sand, sphagnum, or vermiculite. Adventitious buds and roots form at the base of the petiole.

IN GRAFTING, one inserts a part of one plant into or upon another in such way that they become united and continue to grow. The cambium layer of each part must unite with the other.

The part with established roots is called the stock or understock. The shoot portion of the desired variety is called the scion.

Graftage is a term applied to scion grafting, inarching (or grafting by approach), and bud grafting.

There are limits within which successful unions may be accomplished, but the range is greater than one might expect. Plants having true bark cambium and pith, known botanically as exogenous plants, may be grafted. Good results may be expected, in general, within the same genera, quite frequently within the same family, and less frequently between different families. Grafts between species are sometimes called heteroplastic grafts.

Interesting examples of heteroplastic grafts include white sweetclover (Leguminosae family) grafted on sunflower stock (Compositae) and geranium (Geraniaceae family) on smoking tobacco (Solanaceae family). Cowpeas can be grafted on tomatoes, clover on geranium, and tomato on geranium.

Pears are grafted on quince rootstocks to produce dwarf pears. Lilacs may be grafted on ligustrum. Plums are often grafted on peach rootstocks.

There is an almost limitless number of successful heteroplastic grafts.

Of the several kinds of grafts, the most used are whip (or tongue) grafts for joining scion and root; veneer grafts (for joining scions to growing plants); and inarching (to unite two growing plants).

A whip graft is prepared by inserting a fitted scion into a notched rootstock in such way that the growing cambial tissues or cambium of the scion and root are alined so closely that they may grow together. The scion may be matched to one side of the root only and does not need to correspond in diameter to that of the root which is often larger. After fitting the scion and root together, the graft is tied with waxed grafting cord or a rubber or plastic grafting band.

A veneer graft is prepared by cutting out a small section of the stock and replacing it with a fitted scion. The graft is tied in the same manner as the whip graft.

Inarching, or approach grafting, is accomplished by removing a small piece of bark from each of two scions that are growing on their own roots (as would be the case of two potted plants), joining the two cut surfaces together, and tying them with waxed cord. It provides a convenient means of maintaining the scion in fresh condition when the uniting process is expected to be somewhat slow.

Stocks for grafting are selected to obtain certain objectives. The propagator may be seeking such desirable characteristics as root vigor, disease resistance, transplantability, or maybe dwarfness.

Whip grafts are usually prepared from dormant scions cut from the past season's growth. The scions are stored until midwinter or until they are ready for grafting. Stocks are dug in the fall after the leaves have fallen and are placed in storage until needed.

Veneer grafts may be made in the summer or winter, depending on species and suitable scions. Most conifers are grafted in winter. Most hollies and yews are grafted in early spring.

IN BUDDING, one inserts a single bud into an incision beneath the bark of a stock. It usually is done while the stock is growing in the nursery row and when the bark parts easily from the underlying wood tissues.

The budder may desire to do his budding in the early spring by inserting buds that were formed the previous season. He usually chooses periods in the summer or very early autumn and uses buds that were formed on wood that grew the same season.

Previous-season buds, especially roses, are stored as "bud sticks" over winter and are thus available for use in the spring before new buds are available.

Buds can be attached to stocks in a number of ways.

Shield budding is the commonest and perhaps the easiest method. Bud sticks are selected from the vigorous shoots. They are scions with leaves and buds attached, except in the case of budding in early spring where leaves have been removed for storage or by freezing.

Leaves are removed by cutting the petiole off at the base of the leaf. A short stub is left by which to hold the bud during insertion.

Bud sticks are prepared at the time of budding, if possible, and must be kept moist by wrapping in damp cloth or several thicknesses of damp paper or moss. Stocks in the nursery row are made ready by removing leaves and small branches, which may hinder the work of the budder. If a few leaves are left to shade the bud, there is less danger that it will dry out before a union is effected.

A successful budder is a careful workman. He uses a sharp, clean knife. He cuts through the bark only at a point as close to the soil as possible and makes a T-shaped incision in the stock. He folds the bark on both sides of the vertical cut back to make room for inserting the bud. A bud surrounded by bark (and sometimes a small bit of wood beneath) is removed in the form of a shield from the bud stick and is inserted into the T-shaped incision of the stock. If the bud is a bit too long, it is cut to fit in such manner that the bark of the stock will fold over the bark of the shield. The bud is held in place by wrapping with a rubber strip or raffia, starting just below the bud and increasing tension around the stock above the bud until the area of incision is well closed. Five turns around the stock, if well placed, will hold the bud.

Stocks 1 to 3 years old or more are used for budding, depending on species and conditions. As a rule, 1-year wood is easiest to handle. The top of the stock is removed the following spring when the bud has started to make growth. Sometimes, when the bud grows slowly, the top of the stock is removed in spring to force growth of the inserted bud.

Many fruits, including the peach, cherry, plum, and (in some localities) apple and pear, are propagated by budding. Many ornamentals, including field-grown roses, are budded in summer.

IN LAYERING, we remove plant parts that have been stimulated to produce roots while they are still attached to the parent plant. Some plants tend to form natural layers. Others may be induced to produce roots from aboveground parts by artificial means.

Layering is done easily by covering stems or side shoots of a plant with a suitable medium, such as moist sand or soil. Some plants, like the gooseberry, are layered by removing a greater part of the top growth and mounding the plant with soil. Roots will strike along the buried stems. With some plants, one has to pin the stem to the soil with pegs or hold them in place with a brick or stone after the stem is covered.

Raspberries are propagated easily by pegging the tips to the soil while the plant is growing vigorously.

Grapes, clematis, and other vining plants may be increased by looping a stem or cane so that it comes in contact with the soil in several places. The stem has to be pegged tightly at each point of contact. Rooting is often stimulated by cutting notches or rings or by twisting the stem at the point it touches the soil.

A PROBLEM in vegetative propagation is the need to maintain vigor and prevent the degeneration of stocks.

Degeneration is any disorder that reduces the vigor or productivity of plants during subsequent series of propagations.

The use of a part of an established plant for starting new plants may result in degeneration of the stock if the established plant suffers from certain diseases, insects, nematodes, or abnormalities.

Nowhere do the expressions "like father, like son" or "a chip off the old block" apply more exactly than in vegetative propagation. For the "chip" to be healthful, the "block" must be healthful.

Preventing degeneration, or running out, of vegetatively propagated stocks is highly important in the cultivation of crops that are vegetatively propagated.

Degeneration may result from infection by diseases (virus, fungus, bacteria), by genetic mutations, by infestation with nematodes and insects, or by varietal mixtures.

Virus diseases and genetic mutations probably are the most fearsome causes of degeneration in plants, as they are irreversible and usually are difficult to detect and identify. Once a plant is infected with virus, all plants propagated from it are usually infected. Most viruses weaken plants. A virus is a transmissible infectious agent, too small to be seen by a compound microscope, that multiplies within the cells of a suitable host.

Some mutations are inconspicuous. Others are spectacular, as when leaves become streaked or variegated. Variegated (for example, Blakemore strawberry with June yellows) plants are frequently unproductive and worthless.

Viruses may be spread by the handling of infected material and by insects and nematodes. The most important operation in the production of some crops may be to prevent the spread of viruses during propagation of plants. That usually requires rigid control of insect vectors by using insecticides or by isolating plants from sources of disease.

We cite strawberries as an example of how degeneration is avoided in a vegetatively propagated crop, although peaches, potatoes, chrysanthemums, lilies, and other crops could be used as examples.

Strawberries are vegetatively propagated by runners (stolons). Each runner plant is like its mother plant. Any diseases the mother plant has may be passed on to the runner plants. Aphids, cyclamen mites, two-spotted mites, and nematodes, all harmful to the plants, are passed along from plant to plant during propagation.

Aphids are particularly harmful. Some kinds carry viruses and in a few days may cause untold damage by spreading virus from a nearby field of infected plants into virus-free stocks.

Most viruses in strawberries cause a weakening and degeneration of the stocks without any distinctive foliage symptoms in plants of cultivated varieties. Indexing is grafting a part of one plant to part of another plant that is very sensitive to virus. Only by indexing to Fragaria vesca, a wild species of strawberry, was the presence of viruses established.

Shortly after the Second World War, investigators discovered that most stocks of strawberries in the United States were infected with viruses, as shown by indexing to Fragaria vesca.

The discovery led to an extensive search for the most vigorous plants of each variety. They were indexed, and some were found free of virus. The virus-free plants were propagated, first by research investigators and then by commercial nurserymen, under conditions that would insure substantially virus-free stocks. The new plants then were distributed to growers.

Certain precautions to prevent reinfection by viruses were taken by nurserymen during the propagation of the substantially virus-free stocks. These included isolation at a considerable distance from other strawberry stocks and applying an insecticide (malathion) frequently to control aphids.

Some States with large strawberry industries have adopted regulations governing the production of virus-free plants based on the principle of periodic replacement of stocks with new virus-free plants. Each State maintains indexed virus-free stocks in screen-houses to furnish new stocks to the nursery industry. Thus they prevent degeneration from virus diseases.

Parasitic fungus diseases can devitalize nursery stocks. If the fungus is soil-borne, such as Verticillium, control may be difficult.

Chrysanthemum stocks infected with Verticillium can be freed of the disease by removing rapidly growing tips, rooting them in sterile sand or soil, and growing them in field plots free of Verticillium. Contaminated soil can be freed by fumigating with chloropicrin or methyl bromide by modern machine methods.

Modern fungicides can be used to reduce or eliminate some devitalizing airborne fungus diseases and thereby avoid degeneration of nursery stocks. Cyprex is effective against cherry leaf spot, a disease that severely weakens and stunts cherry trees in the nursery, but it cannot be used on trees bearing fruit.

Captan effectively controls leaf spot and leaf scorch of strawberries and prevents weakening of the stocks. Strawberry plants free of the trouble, if grown in isolation, remain free indefinitely.

Crown gall is widespread and especially troublesome in nursery plantings. Infected plants are unsalable. The organisms spread quickly by cultivating and pruning tools and by persons who handle the plants. Control is difficult and consists mainly in treating soil with antibiotics, such as Terramycin, and applying methods of sanitation. Avoidance of alkaline soils is helpful. The detection of incipient infections is difficult. Dipping nursery stocks in antiseptic solutions that will not harm the plants may be helpful.

Degeneration of nursery stocks usually occurs following severe infection from nematodes, the tiny eel-like worms that live on the tops or roots of plants. The stunting and leaf malformations caused by nematodes feeding in the tops of plants usually are conspicuous enough that infected plants can be eliminated by diligent roguing. Incipient infections are difficult to detect, and stocks may be contaminated sufficiently to cause degeneration when the nematode population increases over a period of several months. Sanitation is the chief control unless all plants are infected. Completely infected plants sometimes may be freed of nematodes by subjecting dormant plants to a flash hot-water treatment that kills the nematodes without seriously damaging the plants.

Two general types of soilborne nematodes are parasitic on plants. One type spends its life in direct contact with the soil and feeds on roots from the outside. The other type spends most or all of its life within roots.

The former can be eliminated from plants by thorough cleansing of the root system. The latter require special treatments, such as hot-water treatment or rooting aerial parts of plants in disinfected sand or soil.

Fumigation of soils to rid them of nematodes is an important part in preventing degeneration of stocks.