Humans started bringing plants indoors in the middle of the last century, when Victorian English gentry stuffed their parlors with ferns, palms and aspidistras.
Ever since, we've appreciated a plant's gifts of beauty, serenity and the sense of worth and purpose that comes with the responsibility for keeping something alive--even a sulky philodendron.
But now, thanks to National Aeronautics and Space Administration research, we can appreciate indoor plants for much more than aesthetics and duty: They keep us healthy by purifying our air.
And not just stale, tobacco-clouded air. Since the energy crisis of the '70s, in order to reduce heating and air-conditioning bills, buildings have been constructed with more insulation, unopening windows and recirculating air systems.
This, coupled with building materials that have proved downright toxic, have given us the "sick building syndrome"; gases emitted by such homes and offices can cause sore throats, stuffy noses, skin rashes, headaches and other miseries. Add radon to all that, and our homes and offices could be killing us.
This problem was of particular interest to NASA, because it applies to many closed environments, including space stations. Experiments by B. C. Wolverton at the John C. Stennis Space Center in Mississippi show that common house plants--pothos, spider plant, English ivy, Dracaena marginata --remove deadly benzene, formaldehyde, trichloroethylene and carbon monoxide from the air.
Carbon monoxide comes from auto emissions, or at least most of it, but the other three are also with us just about everywhere: benzene is a common solvent in gasoline, ink, plastics and rubber, and it's also present in some detergents, drugs and dyes.
Benzene can cause blood and bone-marrow diseases and many less drastic ailments, such as tension, headaches and sleepiness.
Formaldehyde is no longer confined to biology lab jars; foam insulation, paper products (from grocery bags to tissues), particle board, permanent-press fabrics, adhesives, cigarette smoke and kerosene all contain formaldehyde. Most mobile homes are chock-full of it because of the materials used in construction.
Formaldehyde can cause asthma, throat cancer and skin, eye and nose irritation.
Trichloroethylene is big in dry cleaning, paints, varnishes and adhesives. It also causes liver cancer.
The amazing thing is that plants don't keel over after wheezing this stuff into their systems; they somehow absorb the poisons through their roots and transform them into clean oxygen, which is released into the air for us to breathe.
According to Wolverton's research, any plant will help, even a fleshy succulent like aloe vera, but those plants that absorbed the most unhealthy air (in a sealed room with one plant in a 6-inch pot of soil) were Gerbera daisy ( Gerbera jamesonii ) , popular with the florist trade and not commonly considered a house plant; English ivy ( Hedera helix ) , mother-in-law's tongue (Sansevieria laurentii ) , pothos ( Epipremnum aureus ) and spider plant ( Chlorophytum elatum ) .
Dracaenas and palms did well, even a banana plant. Different plants were tested with different chemicals, and some absorbed one poison more readily than another; the main point is that they all absorbed something.
An important point: In Wolverton's research, the soil is almost as important as the plants in the purification process; the experiments indicate that the soil should be open to the air, not shrouded by greenery (and not covered with bark or pebbles).
Wolverton also conducted studies of plants and soil combined with a carbon filter and recirculating fan; this was an even better purification system, but until this setup is easily (and inexpensively) duplicated for home and office use, a plant in potting soil will do a good job.
While NASA's report is suitably scientific, the results are simple enough: Living and working with indoor plants will keep humans healthier than living and working without them.
And for people who toil in one of those hermetically sealed new buildings, plants should be a part of the operating budget, like pencils and fax machines. Wolverton says that eight to 15 plants will "significantly improve" the air quality in an average home; that's about one plant per 100 square feet.