The leaves are absorbing carbonic acid from the atmosphere, and the roots are drinking in water from the soil.
What becomes of the carbonic acid?
How is the sap disposed of?
What does it contain?
How does the plant obtain its carbon?
Its oxygen and hydrogen?
Its nitrogen?
Its inorganic matter?
Under the influence of daylight, the carbonic acid is decomposed; its oxygen returned to the atmosphere, and its carbon retained in the plant.
The water taken in by the roots circulates through the sap vessels of the plant, and, from various causes, is drawn up towards the leaves where it is evaporated. This water contains the nitrogen and the inorganic matter required by the plant and some carbonic acid, while the water itself consists of hydrogen and oxygen.