Ultrastructure, Histochemistry and Notes on Germination Stages of Spores in Selected Mosses

Ultrastructure, histochemistry and sequence of germination phases in mosses have been studied in three isosporous species, viz. Polytrichum commune Hedw., Ceratodon purpureus (Hedw.) Brid. and Funaria hygrometrica Hedw. and in one anisosporous species, Macromitrium sulcatum (Hook.) Brid. In each the aperture region is characterized by: 1. drastic thickening of the intine, 2. decrease in thickness of the exine, 3. lamellate structure present subjacent to the thin part of the exine and 4. accumulation of electrondense material into a thin separating layer between the intine and the exine. Further, in P. commune, a knob-like structure associated with the thickened part of the intine is present. When mature air-dried spores were soaked in tap water in daylight, water was absorbed through the aperture region. The subsequent sequence of stages was observed to be: swelling, spore wall rupturing, protrusion and recovery followed by spore distension. Spore swelling consists of two basically different kinds of swelling: symmetrical and asymmetrical. The symmetrical swelling is a process of remoistening rather than a stage in the germination. The asymmetrical swelling is caused by swelling of the asymmetrical intine which protrudes beyond the exine and perine in the aperture region. The recovery phase, not previously reported for mosses, is characterized by almost no structural changes. During this the protruded protoplast of the spore is protected from the surrounding environment only by the intine wall complex of the aperture region. The opaque zone, previously reported to be present between the intine and exine, originates from the lamellate structure present in the aperture region. As in pollen grains and fern and liverwort spores, we assume that exine formation in mosses occurs by apposition of lamellae of the lamellate