Growth Parameters in the Cotyledon of Date Seedlings

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Abstract
Cotyledon expansion in date (Phoenix dactylifera L.) seedlings was examined in detail during the initial 4 wk of seedling growth. Complete expansion takes ca. 10 wk. The proximal cotyledon region expands by intercalary meristematic activity at the base. Vascular tissue matures first in the junction between the two portions of the cotyledon and continues basipetally. The distal portion of the cotyledon, or haustorium, grows by a dramatic increase in volume of intercellular space of internal tissue. Isodiametric internal parenchyma cells expand to form elongated, tubular cells, which appear to be randomly oriented. The surface layers increase mainly by anticlinal cell division and some expansion in the epithelium. At 4 wk, the epithelial cells are rectangular, and a distinct layer of isodiametric cells is appressed to the epithelium. Vascular bundle maturation occurs simultaneously throughout the haustorium.