||P.35: "An easier way for molecules to move between plant cells is by means of the plasmodesmata (singular: plasmodesma). These are fine, membrane-flanked, cytoplasmic threads that pass from a protoplast, through a pore in the cell wall, directly into the protoplast of a second cell (Fig. 1-13). The pores usually occur in locally thin regions of the primary cell wall, referred to as primary pit-fields, which can contain many plasmodesmata. (If a secondary cell wall is deposited, openings in that wall occur in the regions of the primary pit-
fields.) Plasmodesmata can be 50 nm in diameter (range, 20 to 200 nm) and typically have a frequency of 2 to 10 per square micrometer of cell surface. They usually occupy about 0.1% to 0.5% of the surface area of a cell."