O

Fig. 7.1 Bilateral spore of Pyrossia nummularifolia. a. Spore before acetolysis showing perine b. spore after acetolysis.

are either bilaterally symmetrical (Fig. 7.2) or radially symmetrical (tetrahedral) (Fig. 7.3).

The surface of the spore facing the centre of the tetrad is the 'proximal surface', and diametrically opposite to it, facing the periphery of the tetrad, is the 'distal surface'. It is often easy to locate the proximal surface in isolated spores, because it is on this side that the laesura is found.

Shape

Shape in the polar as well as in the lateral view of the spore is significant. Pteridophye spores are rarely globose, but the tendency to attain this form is met with both among bilateral and tetrahedral types. The outline of the tetrahedral spore seen in polar view ('amb') is often triangular with either straight sides or variously concave or convex sides.

The amb of the bilateral spore may be 'ovate', 'oblong', elliptical or 'circular'. In the lateral view, the bilateral spore can be most commonly 'plano - convex' (proximal side flat, distal convex) or 'biconvex', the latter being uncommon.

Typically, a tetrahedral spore has a pyramidal proximal side and hemispherical distal side. The proximal side is sometimes flattened to various degrees or may even be concave.

Fig. 7.1 Bilateral spore of Pyrossia nummularifolia. a. Spore before acetolysis showing perine b. spore after acetolysis.

spore.

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