one of the minute apertures between the cells in many serous membranes.-the minute breathing pores of leaves or other organs opening into the intercellular spaces, and usually bordered by two contractile cells.-the line of dehiscence of the sporangium of a fern. it is usually marked by two transversely elongated cells. see illust. of sporangium.-a stigma. see stigma, n., 6 (a) & (b).