How does gaseous exchange occur in roots ?

Mature roots are sheathed in layers of dead cork cells impregnated with suberin — a waxy, waterproof and airproof substance. So cork is as impervious to oxygen and carbon dioxide as it is to water. However, the cork of both mature roots and woody stems is perforated by nonsuberized pores called lenticels. These enable oxygen to reach the intercellular spaces of the interior tissues and carbon dioxide to be released to the atmosphere. Once oxygen and carbon dioxide reach the network of intercellular air spaces, they diffuse rapidly through them.