New Zealand practices in the propagation under glass of woody plants by seed and cuttings : A thesis submitted in partial fulfilment of the requirements for the National Diploma in Horticulture, N.D.H. (N.Z.)

Abstract

The propagation of plants, particularly trees, by means of cuttings was discussed by Theophrastus in his Enquiry Into Plants (1), written about 300 B.C. Pliny’s Natural History described the propagation of numerous species by various methods, including the use of seed and cuttings (1). Indeed, the history of plant propagation is not a story of new methods but rather one of continuous development of techniques already in use. Advancement in the propagation of plants by cuttings, especially through the use of young material, was dependent upon the introduction and utilization of glass as an aid in the culture of tender plants. A structure with glass windows in the side walls was erected in the Apothecaries’ Garden at Chelsea in 1684, and in 1717 Switzer published the plan of a “forcing” house which included a glass roof (2). It was not until the 19th century, however, that propagating houses and pits were built, and the practice of increasing hardy trees and shrubs by cuttings of immature wood inserted in heated glasshouses seems to have been slow to evolve. Later developments included specialised propagating houses, frames, and bottom heat. Use of the latter has been simplified by the introduction of electricity to the glasshouse in recent years. With the advent of mist propagation, growth-stimulating chemicals (or hormones), and various plastics, a greater amount of progress has been made over the last thirty years than occurred over any comparable period in the past. Much work remains to be done, especially with hormones and plastics, and future developments in the use of controlled light and photoperiod—at present in the early experimental stage—open up exciting new possibilities for the advancement of propagating techniques in the immediate future. Most of the available literature on plant propagation relates largely to indigenous conditions of the Northern Hemisphere. The New Zealand propagator not infrequently finds that somewhat different techniques and modifications of Northern Hemisphere practices can be applied in this country with beneficial results. The purpose of this thesis is to discuss aspects of the title subject as they concern New Zealand horticulturalists. Throughout this thesis I have assumed the term “glass” to also cover certain glass substitutes.