While the term canopy is popularly used to describe the leafy foliage of the vine, the term actually refers to the entire grapevine structure that is above ground. This includes the trunk, cordon, stems, leaves, flowers, and fruit. Most vine training deals primarily with the "woody" structure of the vine-the cordons or "arms" of the vine that extend from the top of the trunk and the fruiting "canes" that extend from the cordon. When the canes are cut back nearly to the base of the cordon, the shortened stub is called a "spur". Grapevines can either be cane trained or spur trained. In cane training, the grapevines are "spur pruned" meaning that in the winter the fruiting canes are pruned essentially down to their spurs with over 90 percent of the previous year's growth (or "brush" as it is known) removed. Examples of cane training systems include the Guyot, Mosel arch and Pendelbogen. Conversely, spur trained vines are "cane pruned" meaning that the individual canes are relatively permanent with only excess buds at the end of the cane being removed.Cordons are trained in either a unilateral (one arm) or bilateral (two arms) fashion with the latter resembling the letter "T". The cordons of grapevines are most commonly trained horizontally along wires as in the Lyre and Scott Henry systems. However, notable exceptions do exist, such as the "V" and "Y" trellis systems which elevate the cordon to various angles that resemble their namesake letter. Note that vertical trellising systems, such as the VSP system often used in New Zealand, refer to the vertical orientation of the fruit canes in an upward manner and not the cordon "arms" of the vines.From the cordon, plant shoots emerge from the bud that eventually develops mature bark and becomes the fruiting cane from which grape clusters will emerge. These canes can be positioned and trained to whatever angle is desired by the grower. Typically, they are positioned upwards but they can be bent into an arch such as a Pendelbogen or Mosel arch system, or trained to point downwards such as the Scott Henry and Sylvos system. The latter method requires more labor-intensive trellising and training for Vitis vinifera vines which are naturally more inclined to grow upwards rather than down. In systems such as the Scott Henry, this downward growth is achieved by the use of movable wires that first allow the canes to grow upwards until about 2 to 3 weeks before harvest when they are then shifted downwards where the weight of gravity on the hanging grape clusters helps keep the canes pointing down.The leafy foliage of a grapevine's canopy will be dependent on the particular grape variety and its propensity for vigorous growth. These leaves emerge from shoots on the fruiting cane in a manner similar to the grape clusters themselves. A vine is described as "vigorous" if it has a propensity to produce many shoots that are outwardly observable as a large, leafy canopy. The ability of the grapevine to support such a large canopy is dependent on the health of its root system and storage of carbohydrates. If a vine does not have a healthy and extensive root system in proportion to its canopy, then it is being overly vigorous with parts of the vine (most notably the grape clusters) suffering due to lack of resources. While it may seem that more foliage would promote increased photosynthesis (and such carbohydrate production), this is not always the case since the leaves near the top of the canopy create excess shading that hinders photosynthesis in the leaves below. One of the objectives of vine training is to create an "open canopy" that allows limited excess leaf growth and allows plenty of sunlight to penetrate the canopy.