In 1986, Waldemar Anguita acquired a patent for a helmet with cactuses inside. The idea behind the greenhouse helmet is quite reasonable, but the execution leaves much to be desired. From the description:
A principle object of the present invention is to provide a greenhouse helmet designed to contain plants secured within and the helmet worn completely over the head of a person so that the person can breathe in the oxygen given off by the plants.
Another object is to provide a greenhouse helmet that has air filters so that ambient air containing carbon dioxide will be filtered therethrough and mixed with the carbon dioxide breathed out by the person to be used by the plants.
An additional object is to provide a greenhouse helmet that will contain hearing and speaking devices so that the person can hear within and speak out through the helmet.
This is literally a terrarium you live in. Exactly how many cactuses would you need to provide the correct amount of oxygen for a human to breathe? I don't even want to imagine the reasons why anyone would want to use such a helmet. If the air around you is so polluted that you need something like this, taking it off to eat or drink or water the plants would be dangerous. But wearing it would be dangerous, too. I prefer to keep my cactus on a windowsill, away from my face. -via Weird Universe