What are pits?
Pits are the characteristic depressions on the cell walls of plant cells. They act as the channels for the transport of water and minerals between adjacent cells. Pits of two neighboring cells are usually located opposite to each other and these opposite pits together are called pit pair. Each pit has a cavity called pit cavity. Pit cavity opens internally to the lumen of the cells. The pit cavities of a pit pair are separated by a thin membrane called pit membrane. Pit membrane composed of the middle lamella and the primary cell wall of corresponding cells.
What are primary pit fields?
Pits of primary and secondary cell wall show considerable differences. Well organized pits can be seen on the secondary cell wall. Pits of primary cell wall look like depressions on the cell wall. These depression like pits on the primary cell wall are called primary pit fields or primordial pits or primary pits. The cells with only primary cell wall, such as the parenchymatous cells of meristem, have only primary pit fields.
The sectional view of a primary cell wall with primary pit fields looks like ‘beads on string’ like appearance. This is because; the primary pit fields are formed as depression on the primary cell wall, moreover, the primary cell wall of primary pit fields is relatively thin than other portions. The wall of the primary pit field is traversed by many plasmodesmatal canals. Plasmodesmata provide cytoplasmic connectivity between adjacent cells. Through plasmodesmata, the protoplasm of living cells are interconnected.