Dear Student,
In angiosperms, anther contains meristematic cells surrounded by an epidermis layer. As the anther develops, these meristematic cells actively divide and become two-lobed. Each anther lobe leads to the development of two pollen sacs. Ths means that two-lobed anther will develop four pollen sacs. These pollen sacs are situated at the four corners of the anther.
Regards