Ruptur der Kapselwand beiSphagnum

Abstract

Two layers of modified cells of the “Wassergewebe” turn the border area of operculum and urn into a rigid zone of resistance. This maintains its diameter, even though the rest of the capsule wall starts to shrivel up once evaporation deprives the mature sporangium of most of its water content. The reinforced capsule area stands out progressively over the collapsing tissue on either side as shrinkage proceeds. Thanks to the presence of this rigid band of capsule wall tissue, the shape of the sporangium gradually changes from a sphere to a cylinder whose perfectly shaped distal mantle edge, naturally, coincides with the zone of resistance. This is where the capsule wall breaks, because the specific type of deformation makes this edge the site of maximum stress. The ensuing rent separates entire cells within the epidermis, while the adjoining layers of subepidermal cells are torn, leaving only a single wall intact, i.e. the inner periclinal wall of the second, innermost layer. The final rupture of this wall, which is still poorly understood as a mechanism, then triggers off the “explosion” of the capsule.