Abstract

Conceptual developments have defined concrete questions about the timing and precise location of cellular pattern formation. Plants in general, and the trichomes of Arabidopsis in particular, are remarkably suited for research on these problems. Genetic analysis requires the quantitative characterizations of the developmental processes by which patterning occurs. Larkin et al.(1) have provided measures of the non‐random distances between trichomes. They have also obtained evidence about the cell lineages leading to trichome development, and this evidence constrains the possible role of intracellular programs. Continued genetic analysis may call for the identification of mutations that are expressed only during development and whose effects are corrected before the phenotype matures.