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Grape Index
Chapter 2. Vine Structure
The grapevine consists of two basic portions; the roots which are normally underground, and the trunk, arms, and shoots which are usually aboveground (Fig. 2-1). The shoots consist mainly of stems, leaves, and flowers or fruit. The cells are the small structural compartments that make up tissues. Since they possess protoplasm (living material), they are the living units of vine structure and function. The vine consists of cells and the product of cells, and is an integrated collection of living and non living cells.

Roots
First Year Growth

Roots differ from stems because they lack nodes and internodes (regions that alternate throughout the length of the stem). The usual method of propagating vines is to use stem cuttings. Roots arise from meristematic regions near the surface of the cutting, and most develop near buds at the nodes. These roots, which do not arise from other roots, are termed adventitious. At the start of each growing season the overwintering roots develop new absorbing roots from many growing points (Pratt, 1974). As the root system develops and enlarges, root branches that arise from meristematic regions inside the root, may in turn produce new branch roots (Fig. 2-2). The finest roots, known as rootlets or feeder roots, are important because they greatly increase the absorption region of the roots.
Fig 2-1. Diagramatic illustration showing important structure and function of grapevine.
At the apex of the roots is the root cap, a mass of cells covering and protecting the apical meristems (undifferentiated tissues who cells are capable of active cell division). Behind the root tip is a zone of elongation a few millimetres long (Pratt, 1974). Proximal to this is the zone of absorption of water and salts from the soil, about 3.4 in (10 cm) long, and many epidermal cells have elongated perpendicularly to the surface to form root hairs that increase the absorbing area. This portion of the root, also known as the root hair region, is often yellowish in color. This zone, constantly replenished by new growth, and the root tip are very important regions of the root because growth in length, most absorption of water and nutrients from the soil, and development of primary tissues (first developed) occur here. Differentiation (development of tissues with many cells for performance of certain functions) begins in the upper cells of the meristemetic region and extends upward through the zone of elongation into the lower zone of root hairs. In California, where soils are almost neutral to slightly alkaline, few root hairs are produced. Proximal to the zone of absorption is the zone of conduction, the mature stage.

Seeds are planted in breeding work to produce new varieties; a taproot develops and laterals arise from it. New roots then grow from the laterals and further branch roots develop.

Penetration and Spread

The root system of grapevines often penetrates deeply and spread laterally in the soil to a greater degree than the tops of the vines. It is a major component of the vine in terms of both absolute bulk and function. It often consists of the third or more of the dry weight of the entire vine. Most of the roots are usually located in the upper 5 feet (1.5 m) of soil, but they can penetrate much deeper, often to 6 to 10 (1.8 to 3.0 m) or more (Kasimatis, 1967). In coarse sands or gravely soils, roots can penetrate 25 feet (7.6 m) or deeper; penetration is usually less as the soil texture becomes finer.

Root depth may be limited by the occurrence of a water table, hardpan (a soil zone impervious to root growth), shallow soils, or by a zone of toxic materials in the soil. The root is structurally adapted for its major functions of absorption, anchorage, and storage.

The Aboveground Part of The Vine

The aboveground part of the vine consists of the trunk and arms, shoots (including leaves, buds, and tendrils), flowers, and fruit.
Trunk and Arms

The trunk is the main stem of the vine that supports the canopy of leaves and other upper vine parts, and is the connecting link between the top of the vine and the roots. Water and mineral nutrients absorbed by the roots are transferred to the foliage, where food is manufactured for nourishment of the whole plant. A portion of these elaborated food materials are translocated downward through the food conducting tissues (phloem) of the trunk to the roots.
The main branches of the trunk older than 1 year are called arms. They bear the spurs and canes kept at pruning for the production of the following year?s crop of wood and fruit.

Shoots

The succulent stem with leaves that arise from a bud is termed a shoot. It is the current season?s top growth. A lateral shoot is one growing out of the main shoot. The shoot is the portion of a vine that bears the flowers and fruit. The shoot tip refers to the apical end [about 6 in. (15.2 cm) long ] where growth in length occurs as a result of cell division and cell elongation. A cane is a mature shoot after it has lost its leaves. Along the canes are slightly enlarged areas called nodes, where buds develop and from which leaves arise. The space between nodes is an internode, which may be short or long. The cane has a spongy pith at its center which, in most cultivated species (except rotundifolia and munsoniana), is interrupted at the node by a woody partition called a diaphragm.
The stems have rays that break up the secondary xylem (wood) into radial blocks (Fig. 2-3). The vessels (water conducting tubes) are very large. There are also tangentially and radially defined blocks of phloem fibers as well as extensive food storage tissues (Pratt, 1974).

It is still unclear whether the stem is a single axis (a monopodium) or a sympodium. The latter theory states that at each node the main axis is carried on by the topmost lateral bud rather than by the terminal bud. In this case, the original terminal growth ceases and a lateral bud develops into a shoot.

Tendrils

Tendrils as well as the inflorescence can be considered to be lateral branches , each having its own specialized origin, structure, and function (Pratt, 1974). Leafless coiling tendrils occur opposite to or alternating with the leaves, and braces the vine by attaching to wires or other vine supports. Nearly all species have discontinous tendrils; two adjacent leaves have tendrils but the third leaf has none. Usually the lower leaves of a shoot have no tendrils. Vitis labrusca has continous tendrils, in which case there is a tendril or flower cluster opposite every leaf.

Buds

Buds develop from meristems axillary to a leaf. According to their subsequent behavior they can be classified as the summer lateral, the primary, secondary , and tertiary buds (Pratt, 1974) (Fig. 2-4). The primary, secondary, and tertiary are grouped together and appear as one bud. Hence, the three buds together are referred to as a compound bud or merely as a bud.

The primary shoot usually develops from a primary bud on the spur or cane. Before the bud goes into a rest period in late summer of autumn, it usually forms from 6 to 9 nodes (Pratt, 1974). Clusters are usually formed opposite the fourth to sixth leaves. In winter the buds are covered with dark hard scales and a soft tomentum. Each bud really consists of three buds: a central well developed one, the primary bud, and two smaller ones known as secondary and tertiary buds (Fig. 2-5). The shoots usually arise from the primary bud, while the other two remain dormant. If the main bud has been killed, however , one of the secondary buds may begin to grow to replace the dead bud.

The lateral shoot or summer lateral arise from the primary shoot soon after the primary shoot begins active growth. The lateral soot produces leaves and , in vinifera grapes, often several clusters referred to as the second crop ; clusters on primary shoots are called the first or primary crop. Sometimes the second crop may make up 25 percent or more of the total crop. Laterals may grow from leaf axils of the summer laterals in the same season.

Some buds, termed latent buds, remain imbedded in old wood. The weak growing shoots that occasionally arise from latent buds are called water sprouts.

A leaf bud produces shoots that bear only leaves; flower or fruit buds contain a shoot possessing both rudimentary leaves and flower cluster. A fruit bud develops into a shoot that usually bears 1-4 clusters located opposite the leaves on the lower part of the shoot. In the dormant season the various types of buds can be identified only by microscopic techniques
Leaf

The three parts of the leaf are the blade, the petiole, and two stipules. The latter are broad, short scales arising from the enlarged base of the petiole that partially encircle the stem. The pair of stipules can be seen on young leaves early in the growing season, but they soon dry up or fall off. About 30-40 days are required for full expansion of the blade, and senescence begins about 4-5 months after unfolding in full sunlight (Pratt, 1974). Leaves also thicken with age. There are few or no stomates (small openings on leaves) in the upper epidermis (outer layer of cells), but the lower epidermis cells) consists of overlapping platelets of ?soft wax? containing hydrocarbons, esters, aldehydes, alcohols, and unknown acids.

The palisade cells consist of one layer of cells containing many chloroplasts (Fig. 2-6). The spongy mesophyll cells are lobed cells containing many small chloroplasts and numerous air spaces.

The leaf blades are usually indented and most have five lobes. The shape of the leaves is sometimes helpful in varietal identification. Deep indentations between lobes are termed sinuses. The sinuses located at the junction of the petiole and the leaf blade is known as the petiolar sinus. The Margins of grape leaves are also often toothed. The tips of the lobe serrations end in hydathodes, structures which release liquid (p. 32). The primary functions of the leaf are photosynthesis and transpiration.
Flower

The flower and fruit comprise the reproductive parts of the vine. An inflorescence (flower cluster) is initiated during late spring and summer preceding the year in which flowering and fruiting occur. The cluster occurs opposite a foliage leaf in the same position as a tendril, to which it often shows transitional forms (Pratt, 1971). The flowers usually bloom about 6-10 weeks after the beginning of shoot growth, depending on climatic conditions. Flowers are born in cluster or bunch. The rachis is the main axis of the cluster, and the individual flowers are born on a pedicel or cap stem. The portion of the rachis from the shoot to the first branch of the cluster is termed the peduncle.

The main parts of a complete flower are the calyx, usually with five partly fused sepals; the corolla with five green petals united at the top to form a cap or calyptra, which falls at blooming; five stamens consisting of the filament and the pollen-producing anther, and a pistil (Fig. 2-7). The pistil consists of three parts: a stigma, a short style, and an ovary with two locules.

Most vinifera varieties have perfect or hermaphroditic flowers that have both financial pistil and stamens (Fig. 2-8). Female or pistillate flowers have stamens that are short and more or less reflexed, and produce pollen that is generally sterile. These types are found in many varieties of European grape as well as in certain American varieties. Male or staminate flowers have an undeveloped pistil that has neither a sigma nor a style, but contains only a small ovary which cannot be fertilized.

Many species of grapes such as some rotundifolia are dioecious. These have male flowers (functionally staminate) on one plant and female flowers (functionally pistillate) on another. To cultivate such varieties they must be interplanted; usually however, only plants having hermaphroditic flowers are selected for cultivation.

Pollination. During bloom, pollen grains fall upon the stigma where, under favourable conditions, they germinate. Anthesis occurs mainly between 6 and 9 A.M. with a rising air temperature, although much many also occur from 2 to 4 P.M. The pollen tube penetrates the tissue of the stigma, and grows down the style to the embryo sac in the ovary where fertilization occurs. Fertilization occurs 2 or 3 days after pollination (Pratt, 1971). The ovary then develops into the grape berry.

Fruit

Clusters consist of peduncle, cap stems, rachis, and berries. There are various types of bunch shapes such as cylindrical, (same thickness from top to bottom), conical or pyramidal, or globular or round branches (Fig. 2-10).
The berry consists of skin, pulp, and seeds (Fig. 2-9). The skins comprise about 5 to 12 % of mature grape cluster (Amerine and Joslyn, 1970). The bloom is a thin, waxlike layer on the skin that enhances the appearance of the berry and prevents water loss and mechanical injury. The outer layers of the berry, mainly the skin, contain most of the aroma, coloring, and flavoring constituents. The skin to pulp ratio is greater in smaller berries than in larger ones. Thus, a ton of a small berried variety of grapes would have more color and flavor than a ton of the same variety with larger berries (Singleton, 1972). This is one of the reasons that large berried varieties such as Emperor, Ribier, and Malaga do not produce good wines. Different varieties of grapes often have berries of different shapes, which is useful in varietal identification. (Fig. 2-11).

The pulp or fleshy pericap is the portion surrounded by skin in which the seeds are embedded. The juice accounts for 80-90 percent of the crushed grapes (Amerine and Joslyn, 1970). The flesh of most grapes is translucent with colorless juice; in some varieties, however, the pulp is light or dark red. White wines are made from varieties with colorless juice that may or may not have red pigment in the skin. Red wines are made from grapes with red pigment in the skin or pulp. Grapes with red juice are used only for making red wine.

The skins of the European type grape adhere strongly to the flesh so that they are eaten together, but American varieties have slipskins.

Seeds consist of 0-5 percent of the weight of the crushed grapes (must) (Amerine and Joslyn, 1970). Seed number usually varies between zero and four per berry. Seeds are high in tannin (5-8 percent) and oil (10-20 percent of the weight of the seeds).

The stems of the cluster include the rachis and its branches, and pedicels, and make up 2-6 percent of the total weight of the cluster at maturity, depending on variety. There is much varietal difference in length of cluster parts, toughness, strength of pedicel attachment to berries, and rate of drying and browning of stems after harvest. These cluster characteristics are especially important with table grapes, which must be packed and shipped over long distances to market.

Freshly harvested stems sink in water, but after a drying period they float on water. As the cluster frameworks dry, pockets of air are probably retained in the tissues, reducing their specific density and causing them to float.

A ton of grapes can produce about 180-195 gal (681 to 738 liters) of wine depending on variety, type of processing , and other factors.

Continue to Chapter 3