Roots with velamen of three orchids were examined for mycorrhizal infe
ction: an epiphytic orchid Stanhopea tigrina, a lithophyte Dendrobium
kingianum and a terrestrial Epidendrum radicans. Approximately 50% of
all exodermal cells were passage cells that remained non-lignified. Lo
ng cells of the exodermis were lignified, but not suberized. A similar
proportion of passage cells was infected in young and old root sectio
ns. Most coils were located in the three cell layers of cortex beneath
the exodermis. A larger proportion of coils was collapsed in the olde
r part of the roots of D. kingianum and E. radicans.