B lntine

Ektexine-Endexine-

Tectum Columellae Foot layer

□c

Angiosperm Spore Wall
Exine

Fig. 13.6 Wall structures and surface ornament found in spores and pollen grains (diagrammatic). (a) The wall structure in the extant Lycopodium. (b) Wall structure of the extant genus Anemia (Anemia). (c) Tectate wall of angiosperm pollen. (d) Wall structure and surface ornament of angiosperm pollen. The latter terms are also applied to the surface ornament of spores. Abbreviations of the sporoderm layers: EN, endospore; PE, perispore; OEX, outer exospore; IEX, inner exospore. ((a) After Uehara et al. 1991; (b) after Schraudolf 1984.)

Exine

Exine

Fig. 13.6 Wall structures and surface ornament found in spores and pollen grains (diagrammatic). (a) The wall structure in the extant Lycopodium. (b) Wall structure of the extant genus Anemia (Anemia). (c) Tectate wall of angiosperm pollen. (d) Wall structure and surface ornament of angiosperm pollen. The latter terms are also applied to the surface ornament of spores. Abbreviations of the sporoderm layers: EN, endospore; PE, perispore; OEX, outer exospore; IEX, inner exospore. ((a) After Uehara et al. 1991; (b) after Schraudolf 1984.)

functions as the germinal exit in many bryophytes. Spores lacking any apparent dehiscence structures are termed alete.

The development of a multilayered wall structure of spores and pollen is markedly different and the two may not be homologous (Fig. 13.6). The inner cellulose layer, or the endospore, rarely survives fos-silization, the exospore is either a single layer or multi-layered and consists largely of sporopollenin. The perispore is external to the exospore and is composed of sporopollenin material that is more electron dense than the exospore. The wall of many fossil spores (the sporoderm) has only one exine layer. Where two layers are present they can be in contact (acavate) or are separated to varying degrees (cavate). The cavum is most commonly developed in a distal or equatorial position. The layers may be homogeneous or finely lamellate. The layers can be uniform in thickness or variably thickened. A continuous equatorial thickening is known as a cingulum; a continuous equatorial flange is a zona. Spores with composite equatorial features are termed cingulizonate. Discontinuous equatorial features usually developed in the radial areas are valvae (smooth) and auriculae (ear-like thickenings commonly fluted). The inter-radial areas can also develop flanges, coronae or kyrtomes.

Spore surface sculpture is equally diverse with the descriptive terms also applied to pollen grains. The superficial sculpture of the exine is of considerable importance in the description and classification of spores and pollen grains (Fig. 13.6d). In atectate spores and pollen the surface may be smooth (psilate or laevigate), covered with small grains (verucate or granulate), grooved (fossulate, Fig. 13.13g), with mesh-like sculpture (reticulate), with fine parallel grooves (striate), warty (verrucate), with rod-like projections (baculate), with pointed projections (echi-nate) or with club-shaped projections (clavate).

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