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Examining Pollen Grains Size Use an eyepiece micrometer to measure the maximum dimension of several grains to obtain a mean.  Pollens have a large range of sizes, Hazel is used as a reference (32 micrometers). Shape Pollen grains are three dimensional but the image produced in the microscope appears as two dimensional.  The shapes seen will fall into the following broad categories:  Round, appearing spherical  Oval, flattened.  The vertical axis shorter than the horizontal (like a tangerine)  Oval, elongated. The vertical axis longer than the horizontal but still retaining an appearance of roundness.  Long.  The vertical axis much greater than the horizontal (like a grain of rice)  Triangular.  Semicircular.  Bean or boat-shaped.  Multisided.  Often a grain which is basically round but faceted.  Irregular.  This category accommodates grains not covered by those above. Apertures Areas on the surface where the outer casing, the exine, is either absent or thinned.  They are the points where the pollen tube may emerge during fertilisation.  The number, type and position on the grain are used in identification.  Generally apertures are described as furrows ie. groves in the surface, or pores, circular holes in the surface through which the inner layer of the casing, the intine, often extends to form a hemispherical protuberance. Exine section and surface detail The construction of the outer casing of a pollen grain, the exine, is an important feature, drawings in text books can be misleading however eg:  Very thin exine without any visible variation but which has a netted surface appearance  Thin exine but thickening and projecting over prominent apertures.  Thin exine having a heavily netted surface.  Exine beaded to produce a netted surface. Colour   -  The most obvious feature of pollen.