U.S. Patent No. 4,605,000 (.pdf)
Greenhouses teeming with plants are always enjoyable to be inside, and healthy, too! Thanks to the wonders of plant life, carbon dioxide is converted to oxygen, which, when breathed by a person is converted back into carbon dioxide. The cycle is endless. Now, wouldn't it be wonderful to have a portable greenhouse that you could stick your head inside whenever you needed some oxygen? Thanks to the greenhouse helmet, you can carry a greenhouse wherever you go. Surround yourself with greenery whenever the world becomes grey, drab and short on oxygen. Please note, however, that this helmet is not intended for use on a motorcycle. If you were to crash, you might wind up with a cactus in your eye.