Pollinia and Massulae
In most cases the pollen grains of each tetrad become separated from one another and they lie freely in the pollen sac. In some plants, mostly members of Ericaceae, the pollen grains remain in tetrads even when mature. In certain plants, such as Acacia, the tetrads are stuck together as groups, which may contain as many as 64 pollen grains. In some other plants, such as members of the Asclepiadaceae, all the pollen grains of a sac are united in a single compact mass such a mass is termed a pollinium. In some members of the family Orchidaceae the anthers produce groups of pollen grains which are loosely jointed among themselves, usually by means of viscin threads. These groups are called as massulae.