Distribution of Lateral Roots and Pattern of Lateral Initiation in Pontederia cordata L.

The distribution of lateral roots or lateral root primordia has been investigated in mature roots and root tips of Pontederia cordata. It is concluded that the regular spacing of laterals along protoxylem-based ranks is a major element of pattern and that there is some coordination of lateral production activity between ranks. Laterals tend to occur in short spiral sequences on the parent root, apparently as a result of a standard tendency for two successive laterals to be produced in the same spiral sense. It has not yet been possible to define precisely the sequence of lateral initiation at the root tip; primordia are produced in acropetal sequence within each protoxylem-based rank, but it is not clear whether or not they are produced in a single acropetal sequence in the root as a whole.