A Wardian case is closed glass house that was invented by Nathanial Ward in 1829. Ward realized that the extreme air pollution in London at the time was killing the tender ferns and mosses he was was attempting to grow outside his home. After observing the water cycle when hatching a chrysalis in a lidded jar, he decided to try growing tender plants this way, sealed from off the noxious air.
Ward quickly discovered that this was an important discovery and began experimenting with glass houses. He also realized that his invention could revolutionize the transportation of exotic plants from far flung locales. Before the use of Wardian cases only 5% of plants would survive the long ocean voyages that were required to import tropical plants. Ward figured out that by transporting the plants in his cases, they would be protected from salt air and spray, and that the plants wouldn't need additional water for the length of the journey. By using Wardian cases, the plant survival rate on long ocean journeys jumped to 95%.
More on terrariums: