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.

AUGUST E. KEHR is Assistant Branch Chief of the Vegetables and Ornamentals Research Branch of the Agricultural Research Service. Before entering Government work, he conducted research in the Department of Horticulture at Louisiana State University. In 1954 he became horticulturist in charge of the Government Research Program of Potato and Onion Improvement at Iowa State University.

FRED P. ESHBAUGH, horticulturist, became Superintendent of the U.S. National Arboretum in 1954. He joined the Department in 1944 as nursery manager of the Soil Conservation Service at Manhattan, Kans.

DONALD H. SCOTT is leader of the Small Fruit and Grape Investigations of the Crops Research Division, Agricultural Research Service. His principal field for many years has been the development of new and improved varieties of small fruits.