How do the stems of a plant facilitate the exchange of gases?

(N/A) $1$. Herbaceous plants: The soft, green stems of small herbaceous plants contain small pores called $stomata$, which facilitate the exchange of respiratory gases between the internal tissues and the atmosphere.
$2$. Woody plants: The hard, woody stems of large plants and trees possess specialized structures called $lenticels$. These are small, raised pores in the bark where cells are loosely packed.
$3$. Mechanism: These structures allow for the diffusion of $O_2$ from the atmosphere into the stem for respiration and the diffusion of $CO_2$ (a byproduct of respiration) out into the atmosphere.