FIGURE 4.

Structure of Polytrichaceae capsule. (A–C,F,H) Atrichum angustatum that lacks stomata in left hand column. (D,E,G,I) Polytrichastrum ohiensis with approximately 100 stomata in right hand column. (A) Long cylindrical red-brown mature Atrichum capsule with inconspicuous calyptra (C) on the top and tapering neck region (arrow) connecting to seta. (B) LM cross section at the capsule urn showing solid capsule wall, developing sporogenous region (S) and circumsporangial space (IS) forming between the capsule wall and spore sac. (C) Base of recently opened Atrichum capsule showing constriction of neck region (arrow) due to drying in circumsporangial cavity and connecting space. (D) Two mature Polytrichastrum capsules, left without calyptra and right covered by calyptra (C). The capsule is wide and green at the base where the calyptra ends and the narrowly constricted area of the apophysis houses stomata (arrow). (E) LM cross section at the constriction with multiple stomata (arrows), subtended by substomatal cavities and associated intercellular spaces (IS), and central conducting strand (CS). (F) LM longitudinal section at the junction between spore sac with spores (S) and neck. A large circumsporangial space (IS) extends just inside the solid capsule wall (CW), along the length of the spore sac and downward into the neck. The conducting strand (CS) of hydroids (H) and leptoids (L) ends abruptly at the circumsporangial space and spore sac. (G) LM longitudinal section at the constriction showing chloroplast rich cells next to spaces associated with substomatal region on the right and the circumsporangial space to the far left. (H) Epidermis with thick walls and cuticle (arrow). (I) Prominent conducting strand in the apophysis with leptoids (L) around hydroids (H). Bars: (A) = 0.5 mm, (B,E–G,I) = 50 μm, (C) = 0.2 mm, (D) = 1.0 mm, (H) = 20 μm.