1. The present paper reports the results of an exploratory investigation of the degree of lability of differentiation of a physiologically specialized, apparently late-determined, ubiquitous plant cell type, the guard cell. 2. To determine whether guard cells could be stimulated to divide, mature foliage leaves of Begonia aridicaulis Zies. were subjected to three types of wounds: (a) a 5-7 mm. razor-blade incision through the leaf, which was allowed to remain on the plant (non-excised), (b) the same type and position of incision, but with the leaf excised at juncture of petiole and lamina and placed abaxial side down on moist vermiculite in a partially covered glass dish (excised), and (c) leaves cut in half perpendicular to their long axis and the apical half inserted vertically, cut edge down, into moist vermiculite in a partially covered glass dish (leaf fragments). 3. Comparing the three wound methods, uniform results were as follows: (a) Guard-cell division was not observed; (b) the wound-induced division walls in epidermal cells were oriented parallel to the long axis of the wound; (c) the wound-induced division walls proceeded as a wave away from the wound; (d) guard cells degenerated at variable distances from the wound, and this degeneration involved shrinkage of the guard cells parallel to their long axis as well as unequal, and often extensive, deposition of additional wall material and "fragmentation" of the chloroplasts, resulting in their numerical increase, assumption of irregular form, and reduced size; and (e) guard-cell degeneration in both the excised leaves and leaf fragments occurred within approximately the same distance distal from the outermost extent of the wound-induced divisions in the same time interval following wounding. 4. Individually unique results were as follows. In non-excised leaves guard-cell degeneration was conspicuous and occurred at relatively great distances from the wound region. Apparently normal stomata, however, occurred within the region of active division. Although the three subsidiary cells adjacent to the guard cells eventually divided, they did so noticeably later than did regular epidermal cells. In excised leaves guard-cell degeneration was relatively infrequent. The three subsidiary cells next to the guard cells did not divide. In leaf fragments guard-cell degeneration occurred outside the wound-induced division region with intermediate frequency. The three subsidiary cells adjacent to the guard cells divided as actively as surrounding cells with no time lag. 5. It is stressed that (a) the potency of the guard cell and any derivative cells probably can be only elucidated if the guard cell itself can be released from the physical and chemical correlations serving to keep cells in a normal plant morphogenetically stable at functional maturity and that (b) such a problem is simply one facet of a much larger one dealing with potency of idioblastic cells in general.