Question

Different forms of pollen grains.

Answer 1

Explanation:

In some pollen grains, e.g. birch and alder, the two layers of the exine are separated around the pores and form a chamber between the inner and outer exine (vestibulum). Finally there are the so-called bisaccate (pollen grains with "air-bags", e.g. the conifers spruce, pine, Pinus cembra and fir.