The numbers and volumes of cells were determined for consecutive stages in the growth and development of the wheat coleoptile (var. ‘King II’) when grown at 25° C. in darkness from soon after germination to senescence. Cell expansion occurred throughout growth and development up to 96 hours, and was accompanied by cell division between 18–60 hours. Evidence is presented that suggests there are two phases of cell expansion concerned in coleoptile growth. Determinations were made at daily intervals from 24 to 120 hours after sowing of protein nitrogen, trichloroacetic acid soluble nitrogen (TCA-sol. N), ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) in the coleoptile, and the results expressed on a per-coleoptile and per-cell basis. The maximum rate of net protein synthesis took place during or after the cell-multiplication phase of growth, depending on whether the results were expressed per coleoptile or per cell respectively. The ratio of protein nitrogen to TCA-sol. N changed considerably during growth, from 4·7 for young cells to 0·68 for mature cells. The fluctuations in the values for RNA and protein are consistent with the template theory of protein synthesis and the DNA data are discussed in relation to polyploidy in differentiated cells. No significant difference was found in the nucleotide composition of RNA during the growth and development of the coleoptile.