Stomate

Stomate, a transpiration-pore in the epidermis of the sporophyte in the higher plants. It is an aperture surrounded by two cells termed guard-cells, which retain their protoplasm - and chlorophyll and change in form so as to open or close the aperture. The aperture communicates with a large intercellular space within the epidermis. The guard-cells result from the division of a single epidermal cell, and are cuticularised on their outer surfaces. Stomates occur on the capsule of mosses, on fern-fronds, and on most sub-aerial parts of flowering plants. They are absent from roots and submerged structures, and aree generally few in number on the upper surface of dorsiventral leaves. On the under surface there may be as many as 600 to the square millimetre. Similar but larger and immobile guard-cells flank an aperture known as a water-stomate on some leaves, by which water from a vascular bundle is exuded, as in Tropaeolum, Alchemilla, some aroids, and many saxifrages. The term "stomate" has been wrongly extended to the large pores of totally different origin on the thallus of the liverworts. The opening and closing of a true stomate is effected by an increased or diminished curvature of the guard-cells, the result, it wonld seem, of their assimilative processes.