EXINE DEVELOPMENT, STRUCTURE, AND RESISTANCE IN POLLEN OF CINNAMOMUM (LAURACEAE)

We report features of sporoderm development of Cinnamomum verum Presl. from the vacuolated stage of microspores through pollen grain maturity. Before microscope mitosis the sporoderm consists of spinules and gemmae separated from the cytoplasm by a channeled onciform zone. When the intine forms, after microspore mitosis, it is highly fimbriated in profile. The surface of the exine, (spinules and gemmae) is covered by a thick (200-300 nm) surface coating. Elements of the surface coating are glycoprotein and connect with filamentous material within the anther loculus. The gemmae may be assumed to increase in number between the microspore period and pollen grain maturity since their frequency per unit area and the surface area of the grains increase. The implication is that sporopollenin is added late as well as early in development. Spinules, gemmae, and straps between gemmae resist acetolysis, but special handling (no rehydration and minimal mechanical flexure) is required in order to retain the spheroidal configuration of exines; otherwise exines are compacted into knot-like masses that are then unidentifiable.