Figure 2.

The presence of mesophyll is essential for normal stomatal responses to light and CO₂ in Tradescantia pallida, and the signal from the mesophyll may be a vapor‐phase ion. A to C, Responses of stomatal aperture to changes in photosynthetic photon flux density and ambient CO₂ concentration observed in intact leaves (A), epidermal peels (B), and epidermal peels placed onto mesophyll tissue (C). D, Responses of stomatal aperture in epidermal peels to activation of a large negative voltage (−860 V) in an electrode placed near the epidermis, with and without a barrier placed between the electrode and epidermal peel to prevent transport of matter without altering the electrical field. Modified from Mott et al. (2008) and Mott et al. (2014).