Lateral root development in a woody plant, Quercus suber L. (cork oak)

The distribution and the ontogenesis of lateral roots have been investigate d in the Mediterranean woody species Quercus suber L. (cork oak). Lateral r oots arose in protoxylem-based ranks and a tendency to clumping was observe d. Three stages are distinguished in lateral root primordium development. L ateral root primordia are derived mainly from pericycle cells. The endoderm is contributed to the initial lateral root development, forming an endoderm al cover that sloughs off with lateral root emergence. The unemerged latera l roots show an incipient layered root meristem; this meristem can be class ified as a closed type meristem. Primary vascular connection takes place wi th the xylem strand opposite the lateral root primordium and the two adjace nt phloem strands. Primary vascular connector elements are derived from per icyclic derivative cells. Vascular parenchyma cells contribute mainly in th e development of the cambium and the subsequent secondary xylem and phloem connector elements. The secondary vascular elements of the lateral root and parent root differentiate in continuity. Vascular connection is discussed in relation to the root vascular plexus described in monocotyledonous and i n some herbaceous dicotyledonous plants. An endodermis with suberized lamel lae is continuous between the lateral and parent root in emerged lateral ro ots.