How does respiration occur in the stems and roots?

The old and mature roots and hard woody stems of certain trees are covered by bark. The bark contains very tiny openings called lenticels. The lenticels enable the oxygen to reach the intercellular spaces of interior tissues and carbon dioxide to be released into the atmosphere. At the base of the lenticels are loosely arranged cells that allow the diffuse gases to pass through them.
Respiration also takes place through the roots of plants. Air is present in the spaces between the soil particles. The oxygen in this air is absorbed by root hairs present on the roots. From root hairs, it is supplied to all the parts of the roots. Carbon dioxide released during respiration is diffused out of the roots through the same root hairs.