orbiculen.

1931 A. Johannsen Descr. Petrogr. Igneous Rocks I. ii. 17 In many glassy rocks there are found certain more or less spherical bodies varying in size from pellets visible only under the microscope..to huge spheres ten feet or more in diameter. These rounded bodies are called spherulites when the constituents are arranged radially..and orbicules when these constituents are in concentric shells.

1956 L. E. Spock Guide to Study of Rocks iii. 26 A few igneous rocks contain orbicules. These are close spherical concentrations of amphibole arranged radially or of biotite in concentric-tangential pattern.

1985 R. Thorpe & G. Brown Field Descr. Igneous Rocks viii. 114 Each orbicule contains a core, commonly an igneous xenolith fragment but sometimes composed of the same granitic material in which the orbs are embedded.

1961 G. Erdtman et al. in Grana Palynologica 2 iii. 9 Orbicules,..‘con-peito-grains’; small granules spread over the exine surface in certain gymnosperms.

1967 Amer. Jrnl. Bot. 54 629/1 The exine and orbicules (Ubisch bodies) were covered by membranes.

1973 Proc. Royal Soc. B. 184 161 No pollenkitt is deposited elsewhere within the anther, not even onto the sporopollenin orbicules.

1987 New Phytologist 105 489 In this stage, the tapetum cells are only surrounded by sporopollenin-containing membranes, the inner tangential one bearing the orbicules.

1998 Internat. Jrnl. Plant Sci. 159 748/2 Ubisch bodies (orbicules) are species-specific bodies composed of sporopollenin and reported only in association with secretory tapeta.