title: Fine structure, pattern of division, and course of wound phloem in Coleus blumei.
abstract: The wound phloem bridges which have developed six days after interrupting an internodal vascular bundle contain wound sieve-elements, companion cells, and phloem parenchyma cells. An analysis of the meristematic activity responding to the wounding clearly demonstrates that three consecutive divisions are prerequisite to the formation of phloem mother-cells. Companion cells are obligatory sister cells of wound sieve-elements, connected to the latter by specific plasmatic strands and provided with a dense protoplast. Six days after wounding most of the wound sieve-elements are still at a nucleate state of development, but already have characteristic P-protein bodies and plastids containing sieve-element starch. Their cytoplasmic differentiation corresponds to the changes recorded during maturation of ordinary sieve elements. Sieve-plate pores penetrate through preexisting parenchyma cell walls, only, and develop from primary pitfield-plasmodesmata. Wound sieve-elements do not connect to preexisting bundle sieve-elements, they open a new tier of young sieve elements produced by cambial activity.
authors.affiliation: Zellenlehre, Universität Heidelberg, Im Neuenheimer Feld 230, D-6900, Heidelberg, Federal Republic of Germany.
authors.forename: H D
authors.initials: HD
authors.lastname: Behnke
authors.forename: A
authors.initials: A
authors.lastname: Schulz