Ultrastructural details of leaf papilla development in the moss Andreaeobryum macrosporum

Projecting papillae ornament the abaxial leaf surfaces of many mosses, including those of the primitive, ectohydric taxon Andreaeobryum macrosporum Steere & B. Murr.. Such papillae presumably create a network of capillary spaces on the leaf surface proper, through which water can be effectively transported, while providing a water-repellent surface for CO 2 uptake at the papillar tips. Although thesuperficial characteristics of such papillae have been recorded frequently with SEM,nothing is knownof their development or ultrastructural organization. Plants collected on limestone outcrops in the Brooks Range, Alaska in June, 1989, were transferred, intact, to culture dishes of vermiculite, moistened with Hatcher's nutrient solution, and maintainedinan environmental chamber with a 1160 lux, 16 h day: 8 h night light regime at 5 C constant temperature. Shoot apices, 1-2 mm long, were excised from both freshly collected and cultured specimens intoa 1% Triton X solution, 1 h prior to fixation in 2% glutaraldehyde plus 2 % paraformaldehyde in 0.1 MNa-cacodylate buffer, pH 7.2, for 4 h at room temperature.