Asexual Propagation: Grafting

In grafting, a freshly cut section of stem with buds, called a scion, is joined to another plant called the stock. The upper stem of the stock is severed and the scion is joined to the lower stem. The scion is securely attached to the stock, and the tissues of the two plants grow into each other, forming a single plant. The scion produces the stems, leaves, and flowers on the new plant and the stock provides the root system.

Grafting combines desirable qualities from one species, such as disease resistance or the ability to grow in waterlogged soils, with desirable qualities of another, such as the ability to produce high quality fruit. Grafting is often used to make fruit trees more vigorous and productive. Bud grafting is a form of grafting in which a single bud cut from a stem is grafted onto the stock. It can be carried out more rapidly than other forms of grafting and is used widely in the nursery industry to propagate hundreds or thousands of plants in a relatively short amount of time. In nature, roots of oak trees of the same species commonly graft together, hastening the spread of diseases such as oak wilt, a fungal disease that kills a variety of oak trees.

Asexual Propagation: Cuttings and Layering

For many plant species, a leaf, section of stem, or piece of root cut from a plant and lightly covered in soil, peat moss, or another growth medium develops a new, independent plant by generating the missing parts. Stimulated by hormones called auxins, a partially buried leaf or piece of stem, for example, develops roots on the buried portion, and a piece of root forms stems and leaves above the soil. Cuttings and layering are widely used for perennial plants, plants that grow back from the same roots year after year. Commercially, cuttings are the most important source for perennials, such as new fruit trees; conifers, including pine and spruce; a variety of shrubs, roses and honeysuckle, for example; and many florist blooms.

In layering, a new plant develops from a stem that is still attached to the parent plant. In nature, the stem simply arches over and spreads out on the ground. The parts of the stem that are in secure contact with the soil develop the roots, stems, and leaves of a new plant. The flexible stems of trailing blackberries, black raspberries, and several other species spread rapidly in this way.

Growers typically layer species that propagate naturally in this way. Layering is also used for plants such as filberts and Muscadine grapes that cannot be propagated easily by other methods. If plants do not layer naturally, a grower can induce them to layer by pinning the stems to the ground. Growers also layer plants by cutting them to the ground during the winter and covering the new spring shoots with soil, a technique called mound layering. This causes new roots to form along the buried lower portion of the new shoots, and new stems and leaves then grow up through the mound of soil. In a few weeks the new plants are cut away from the parent and planted in a garden or nursery. This technique enables a grower to produce many plants from a single parent that has desired traits. Apple trees, currants, and gooseberries are commonly propagated in this way. In air layering, often used with house plants, stems are partially cut and peat moss or sphagnum moss is wrapped around the wound, which is then covered in plastic wrap. A single plant develops from the place where the stem was cut.

Asexual Propagation

Asexual propagation is the production of new plants from the leaves, stems, or roots of a single parent plant. Asexual propagation, which does not require pollination or fertilization, is a rapid method of propagation. It ensures that all of the parent’s genetic material survives even if the parent dies, and it creates offspring, known as clones, with the same traits as the parent plant. Asexual propagation is advantageous when plants are well adapted to a particular environment. Several methods of asexual propagation occur in nature. They have been adapted for commercial use for rapid propagation and to obtain plants that are hard to grow from seeds.

A. Cuttings and Layering
B. Grafting
C. Agamospermy
D. Tissue Culture
E. Propagation from Stems and Roots

Celery

Celery, common name for a biennial herb of the parsley family, a native of Europe but now widely grown throughout the world. The stalks, about 30 to 76 cm (about 12 to 30 in) high in cultivated varieties, are eaten, raw or cooked, as a vegetable or salad. When allowed to grow naturally, the stalks are greenish in color and slightly bitter in taste. They are often blanched during the last stages of their growth by preventing access of sunlight except to the leaves; this process removes the color and the bitter taste, but also some of the vitamins. If allowed to grow a second year, celery sends up flower stalks about 61 to 91 cm (about 24 to 36 in) tall with small white flowers in umbels. The dried fruit of celery is used as a condiment alone under the name of celery seed or ground and mixed with salt under the name of celery salt. Celery seed is also used in pharmacy as a sedative or to disguise the flavor of other drugs.

Celery is subject to attack by several blights, by the tarnished plant bug, and by the larva of the black swallowtail butterfly. In the United States, celery crops are grown principally in California and Florida.

Scientific classification: Celery belongs to the family Apiaceae 

Spinach

Spinach, common name for an annual crop plant, of the goosefoot family, grown for its nutritious and savory leaves. Probably native to southwestern Asia, spinach was introduced to Europe by the 12th century. It became cultivated worldwide and received sudden popularity in the 1920s when nutritionists found it contained iron, vitamin A, and vitamin B2, or riboflavin.

Two varieties of spinach are now grown. Wrinkled, or savoy, spinach can be packaged and shipped without wadding or spoiling and is marketed fresh. Smooth-leaved spinach can be easily washed and is marketed frozen or canned. Spinach leaves are picked from the immature plant when in the form of a rosette close to the ground. Because extended daylight and hot temperature cause the plant to bolt, or draw growth away from the leaves and into a tall, central flower stalk, spinach is best cultivated in cool climates during spring or fall, or in warm climates during winter. Most spinach in the United States is now produced in Texas and California. Spinach is a fast-growing crop, producing harvestable leaves about 40 days after seeding.

Scientific classification: Spinach belongs to the family Chenopodiaceae. It is classified as Spinacia oleracea.

Orach

Orach, common name for a tall annual plant of the goosefoot family, native to Asia. Orach is also called garden orach and mountain spinach. It is cultivated in Europe and North America both as a foodstuff and as an ornamental. Orach grows to a height of 2 m (7 ft). Its furrowed stems bear soft, arrow-shaped leaves and small flowers in crowded clusters. The young shoots and leaves are eaten like spinach. 

Scientific classification: Orach is a member of the family Chenopodiaceae. It is classified as Atriplex hortensis. 

Endive

Endive, also escarole, common name for a plant (see Composite Flowers) having a curly, lettucelike head, with inner leaves that are used in salads. The inner leaves of the plant are sometimes blanched by enclosing the head of the endive in its outer leaves (which normally fall away) or by covering the entire plant with a special tube of paper. The long blanched shoot of chicory is called Belgian or French endive, or witloof.

Scientific classification: Endive belongs to the family Asteraceae