La première feuille des plantules d'orge. I. Morphogenèse, les épidermes

Abstract

This study of the growth of the first leaf was mainly based on epidermal impressions. The cellular arrangements of the primordium found in the caryopsis are already those of the adult blade. Three initiation periods can be distinguished during morphogenesis. The first period consists of the formation of a primordium from the apical growing point. The primordium insertion takes the shape of an incomplete ring around the apex. The second period consists of the initiation of practically the whole blade from an intercalary meristem. At the beginning of this period, longitudinal cellular partitions lead to increasing of the initiation zone and to variations in blade width. The third period includes ligule formation at the bottom of the blade and the formation of the tubular sheath. The sheath grows from a second intercalary meristem as a continuous ring at the level of insertion. The transversal specialization of the tissues takes place immediately after the initiation phase. It is characterized by a basipetal cellular differentiation, more or less early, and results in cellular strand arrangements that are different on each epidermis. Using the foliar area as reference, the stomatal frequency is the same on both faces of the blade.