Introduction

The discovery, about thirty years ago, that orchids could be asexually multiplied by a tissue culture technique (Morel 1960; 1964a,b) has led to an enormous increase in the number of plants, mostly artificial hybrids, in cultivation. Individual clones have been multiplied on a wide scale in many parts of the world either because their flower production can be controlled precisely, to meet heavy seasonal demand, or because of the quality, colour or longevity of their flowers. Since the first successful adaptation of in vitro techniques for the multiplication of Cymbidium clones, many other orchids have been investigated and many selected plants in more than 30 genera have been propagated in this way (Holdgate 1974; Murashige 1974; Morel 1974; Arditti 1977; Sagawa & Kunisaki 1982; George & Sherrington 1984) (Table 1). The reviews of Rao (1977) and Hughes (1981) list nearly twice as many genera but they included reports of orchids grown in vitro from seeds as well as tissue and organ cultures.

More recently it has been shown that, as for other plants, protoplasts can be isolated from the roots, stems, leaf tissue, petals and protocorms of orchids (Teo & Neumann 1978a,b; Pais et al. 1982; Price & Earle 1984; Loh & Rao 1985; Seeni & Abraham 1986) (Table 2). To date orchid protoplasts have been induced to grow and divide in culture but they have not stayed alive long enough to regenerate tissue or protocorms.