Microbial abundance in orchid rhizoplane dif- fered on two investigated plants. Thus, 1g of terrestrialP.appletonianumrootswaspopulatedby 3.570.18 106 bacteria, whereas 1 g of epiphytic P. articulata roots – by 19278.5 106 bacteria. This finding corresponds to our previous results on greenhouse Acampe papillosa Lindl. Associative bacteria populated its aerial roots 30 times more densely than its substrate roots (Tsavkelova et al., 2004). Thus, the aerial roots may serve as a favorable habitat for bacteria due to the presence of the spongy velamen.