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Summary

Concentrations (w/v) of 1–10 ppm kinetin, with or without 1 ppm indoleacetic acid, may retard the germination of Dactylorhiza (Orchis) purpurella seed but increase the rate of growth of protocorms to the point where shoot initials form. Subsequently diurnal illumination enhances the development of the shoot initial. Chlorophyll production is independent of growth factors and occurs most rapidly at temperatures below 15°C. Green shoot-initials undergo further development only after prolonged cold treatment and this stage appear to be independent of growth factors or symbiotic fungi. Similar results were obtained with Coeloglossum viride and Platanthera bifolia.

Goodyera repens, an evergreen rhizomatous species, did not respond to mixtures of kinetin and indoleacetic acid, or coconut milk, but grew well on potato or yeast extracts, or after infection with symbiotic fungi.

Symbiotic development of north temperate orchids occurs on defined media lacking growth factors and is always more rapid than that in any axenic system so far tested.