They planted radioactively labelled seedlings of Plantago major together with non-labelled ones of Festuca ovina into a culture container. In a further experiment, Plantago was inoculated with a fungus. The root systems of both species are easily distinguished morphologically. Orchidaceae are obligatory mycotrophic just like Ericaceae . They have usually no cotyledons which means that a seed can germinate but not develop further than to a few-celled state.
Further development is possible only in association with fungi that provide the nutrient substratum.
Orchids are accordingly parasites if only in the first phase of their life. The fungus becomes superfluous. The endotrophic fungi do usually perish in the course of the plant s development and their remains are absorbed by the orchids. If this host-specific action does not take place, then the fungus spreads and becomes parasitic. That is why only a small percentage of seedlings develops in many orchid species.