This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
These, I think, we may safely assert are the most generally popular kind of fruits for wall-culture, as not only do they succeed where others fail, but if a judicious selection of varieties is planted, a supply of delicious fruit may be maintained over a lengthened period - the Apple in this respect being its only rival. An unlimited collection, however, is generally the reverse of a profitable one, and, unfortunately, this craving for variety was not confined to the present generation of gardeners. For instance, we have a fine west wall capitally furnished with triple oblique cordons. Sixty plants in sixty varieties were planted, but of these thirty at least are comparatively worthless. Far more profitable would it have been to have planted four each of fifteen good well-tried varieties. Of course it is advisable to give some of the newer varieties a trial; but according to my experience, very few of these are superior to the older sorts.
In the southern counties I have seen Pears fruiting freely on north, south, east, and west walls, and of good quality in each instance. It sometimes happens that employers are particularly fond of one or two varieties; and by planting these in different sites, the supply is considerably prolonged. The only varieties I have seen grown profitably on a north wall are Jargonelle, William's Bon Chretien, Seckle, and Marie Louise; and in each instance, despite absence of direct sunshine, clean, good - flavoured fruit resulted. Here we have William's Bon Chretien on south, west, and east aspects, there being no perceptible difference in the quantity or quality of the crops, and by ripening some of the most forward artificially, the supply of this very popular variety was prolonged over a considerable period, and what is satisfactory to all concerned, not a dozen fruits were spoilt. The early and delicious Jargonelle and Beurre Superfine are being similarly arranged. In the case of varieties that keep longer after ripening, it may not be necessary to distribute the trees; as when the crops are heavy, or early ripening is desired, all that is required is to ripen a few dozen artificially - that is to say, in a box of hay placed in a dry heat such as a forcing-house, or failing this, a hot kitchen.
This not only prolongs the season, but really improves the fruit, both as regards quality and appearance, of many varieties, such as Beurre Diel, B. Clairgeau, Duchess d'Angouleme, Flemish Beauty, Josephine de Malines, and Bergamotte Esperen. At the same time, by distribution there is a better chance of securing crops from one or other of the sites.
From experience in midland, southern, and western counties, in addition to the Bon Chretien, Jargonelle, and Beurre Superfine, I can recommend Louis Bonne of Jersey, Marie Louise, Huyshe's Victoria, Glout Morceau, and Easter Beurre for south, east, and west walls. Beurre Diel, B. Clairgeau, B. Ranee, B. Bachelier, B. Hardy, B. Bosc, B. d'Aremberg, Pitmaston Duchess, Thompson's Van, Mons. Leon Leclerc, Marechal de Cour, Doyenne du Cornice, Winter Trellis, Knight's Monarch, Josephine de Malines, Ne plus Meuris, and Bergamotte Esperen, have proved excellent on south and west walls; while Chaumontel and Beurre d'Amanlis I have only had really good from south walls.