NON-SPINY-WALLED POLLEN GRAINS
In cloves the pollen grains show a six-sided, angled cavity and an outer wall which terminates in three slightly pointed, narrowly notched portions, separated by nearly straight walls.
In santonica the pollen grains have smooth, unequally thickened walls, which are strongly constricted at three points, the outline resembling three half-circles placed together.
In elder flowers the pollen grains appear circular or three-parted. The wall is of nearly uniform thickness, even at the constricted part of the grain.
In century minor the pollen grains show three pronounced restrictions. The wall at these points is very thin. In pichi flowers the pollen grains are either circular or three-sided and three-pointed. Inside of each point there is a nearly white pore. In some of the grains the pollen tube has grown out of one of the pores.
In cyani flowers the pollen grains are longer than broad and the cell contents appear to be divided into two end portions and an elevated middle portion.
SPINY-WALLED POLLEN GRAINS
In anthemis the pollen grains have unequally thickened walls constricted in three places. The spines are short, broad at the base, and sharp-pointed.
In arnica flowers the pollen grains show three light-colored pores and numerous short spines.
In calendula flowers the pollen grains show one or more pores, typically three pores. These pores appear as white spots, and the wall immediately over the pore is smooth and thinner than the remaining part of the wall; the spines are very numerous.