This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
The training of trees is in close connection with pruning; the one regulates the form of the tree - the other, the fruiting shoots and spurs. However plain the rules and directions for pruning may be stated, much must be left to the discretion of the operator, and which practice alone can teach. Preserve an equilibrium in the growth of every part of the tree. Be prudent in the use of the knife, and never amputate large branches if it can be avoided; to aim at a medium between excessive growth and feebleness; to remember that to organize fruit buds, every leaf, young shoot, and bud, requires exposure to solar light. Allow nothing to grow except what is required to carry on the proper functions of the tree, furnish bearing shoots, or to extend its branches.
I have frequently expressed my conviction that the European method of training grapes in houses is not the best system for this climate. When the vines are tied to trellises as sloping as the roof, the fruit hangs down clear of the foliage, and is much more liable to be affected by atmospheric changes, such ad currents of air, condensation of moisture, etc., than when protected and partly covered by the foliage as occurs when trained to . perpendicular trellises. The row of plants marked 1 in fig. 4 is confined to about one third of the roof; the glass above this point will throw sufficient light for rows 2 and 8, the former of which I consider to be placed in the most favorable position for cropping1. By this disposition a large training surface is gained, and more fruit may be gathered under a given surface of glass than by the common mode of trellising the roof. A house built on the ridge-and-furrow principle, covering a large surface without being more than 10 feet high at any point, and the vines trained in row to horizontal trellises, would, I conceive, be an admirable arrangement for a grapery.