Gnetales

The pollen grains of Welwitschia are ellipsoidal, monocolpate with smooth exine marked with longitudinal ridges and grooves. Ephedra has ellipsoidal-ridged grains. Welwitschia and Ephedra have ellipsoidal, striate (Fig. 6.18) or polyplicate pollen, which are unique among extant gymnosperms. The pollen grains of Gnetum are spheroidal in shape with an echinate exine that is with conical spines.

Table 6.2 Pollen morphological description in tabular form.

Name Pollen Grains Exine Furrows Intine

Pinus nigra var. poiretiana (Ant.) Aschers & Graebn. Corsican Pine

In 3 parts, body and 2 air-filled bladders, the body an oblate ellipsoid with a roughened dorsal surface (cf. Wodehouse) surrounding the proximal pole and a ventral surface occupied mainly by the attachment of three-parts spherical bladders leaving a smooth area (the so-called 'furrow') in between, the whole usually presented either in long lateral view, symmetrical about the polar axis only or in one or other of the two possible polar views (a) proximal pole uppermost and bladders below or (b) distal pole, 'furrow' and bladders uppermost and proximal pole below. Body of grain rather large or large with polar axis 41.6 (37.450.0) mm and axes of the ellipse seen in polar view 49.5 (45.1-56.1) mm and 46 (38.3-51.0) mm respectively, body and bladders together in either view 78.0 (71.489.3) mm

Exine of body thickest over dorsal cap, where ectexine c.1.7 mm and endexine 0.8 mm, and the surface patterned with short bent worm-like grooves and interspersed ridges of similar width (vermiculate), about 10-12 grooves to every 10 mm, external walls of bladders consisting only of locally inflated ectexine, which here forms an open 3-dimensional network c.5 mm deep built up of rod-like bodies, the meshes nearest the surface varying from 1 to 3.5 mm across and not all closed, those below the surface much larger, up to 9 mm across, the bladders bounded internally by the endexine of the body.

One on the distal (ventral) surface, crossing the distal pole between the two bladders, rather ill-defined, width between roots of bladders 8.3 (5.2-11.2) mm, membrane thin, its surface smooth.

Intine of body is variable in thickness, 1.7-9.5 mm.

CHAPTER 7

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