Size and Shape of the Stomata

The general dimensions of the stomata of succulent plants do not appear significantly different from mesic plants. Most of those that we have observed are either only slightly or not at all sunken, but are associated with a deep substoma-tal cavity because of the presence of a multilayered hypodermis below the epidermis. To what extent this cavity lengthens the diffusion path length and increases is not known. 

In Yucca and Nolina at least, the stomata are sunken within crypts which can open and close with finger-like projections (Fig. 5.28). During water stress, the leaves curl and seal the stomata within the crypts. 

In many of the cacti, scanning electron micrographs reveal unsunken surface stomata not too unlike those of most mesic plants. 

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