I think this is what they are referring to.


Fig. 10.3-10. Transverse section of oleander leaf (Nerium oleander). Oleander leaves are a favorite in plant anatomy laboratories because they demonstrate a placement of stomata that has ecological significance. The arrows indicate three stomatal crypts: the crypts are large chambers in the mesophyll, covered with an epidermis that contains stomata as well as trichomes (hairs) that project into the crypt. The epidermis on the exposed surface of the leaf – between crypts – lacks stomata. The narrow opening between the crypt and the atmosphere, combined with the presence of trichomes, causes the air inside the crypt to be rather immobile, even if there is a strong wind blowing over the leaf. Any water molecule that diffuses out of a stomatal pore will spend so much time that there is a high probability it will diffuse back into one of the stomata in the crypt. See following figures for higher magnifications.

http://www.sbs.utexas.edu/mauseth/weblab/webchap10epi/10.3-1...