An old-fashioned dome makes a perfect container for tall plants. This group of insectivorous plants -- Scarlet Belle pitcher plant, purple-blooming Mexican butterwort and Venus fly trap -- grows in sphagnum moss. The raised dome allows insects to enter.
from a site called the terrarium museum This is also known as a Wardian case. Named after some Victorian guy who realised that you could keep plants alive long enough to transport in these glass cases.