Introduction
Orchids are ubiquitous; there are epiphytes,
terrestrial plants with underground roots and bulbs,
and even mycotrophic species. The aerial roots of
epiphytes are covered with a velamen – hygroscopic
tissue, consisted of large dead air-filled
cells. It sucks up and retains water with dissolved
mineral salts and nutrients; provides mechanical
protection, reflects solar radiation, and it is
permeable to oxygen and carbon dioxide (Dycus
and Knudson, 1957; Pridgeon, 1986). Interactions
of orchids with their mycorrhizal fungi, essential
for seed germination are long-time investigated