Secondary phloem in transverse view

A transverse section of secondary phloem and xylem from eastern white pine (Pinus strobus) stem.

1 = secondary xylem (early wood); 2 = cambial zone; 3 = conducting phloem; 4 = old (non-conducting) secondary phloem; 5 = tracheid; 6 = uniseriate ray; 7 = sieve cell; 8 = sieve area (stained blue due to presence of callose around sieve pores); note the progressive increase of stain at greater distances from cambium, indicative of gradually increased blockage of sieve pores with age; 9 = axial phloem parenchyma; 10 = crushed sieve cells in non-conducting secondary phloem