Observations on orchid seed mycorrhizae

Summary In the natural germination of orchid seeds, the fungus undoubtedly contributes sugars, auxins, and growth factors in stimulating the growth of the embryo. However, none of these factors alone are as successful in stimulating germination as they are when combined. No single factor can be identified as the specific germination agent in the mycorrhizal relationship. Seeds can germinate, although poorly and slowly, without added sugars or auxins. Rather, a combination of factors promoting vigorous aerobic respiration provides the cellular environment necessary for germination. Fungus infection in nature, or artificial media in the lab, can provide these conditions: either rapidly by providing exogenous substrates and growth factors for respiration; or slowly by stimulating the utilization of endogenous lipid seed reserves. In either case, cell division and synthesis of chlorophyll follow. A speculatory metabolic pathway is outlined.