Oxygen in plants

1161. Oxygen. The proportion of oxygen in plants is, generally speaking, less than of the carbon, but it is equally essential to their existence, there being very few vegetable substances which do not contain more or less of it. Plants always absorb by their roots more oxygen than they are able to assimilate, taking it in combined with carbon or carbonic acid gas, and united to hydrogen as water; hence a growing healthy plant is constantly exhaling this superfluous oxygen.