The end walls of sieve-tube elements in the phloem have 4-6 specialized sieve areas which together form compound sieve plates.
韧皮部中筛管分子的端壁是由4—6个梯状排列的筛域组成的复筛板。
2
The tracheid and sieve tube elements are all differentiated from the procambia in the center of the haustoria, and the former occurs prior to the latter.