Embryo- und Wurzelentwicklung bei Coix lacryma-jobi L. (Gramineae)

Summary Homology of the first embryonal root of Gramineae has been argued by many botanists. The main reason of the controversy is that they have no agreement on the definition of the exogenous and endogenous root development. The present authors do not use the definition by Brown (1965) after whom all roots of all plants are “endogenous”, because their apical meristem is covered at least with a root cap. Another definition by Troll (1949) and Guttenberg (1960) is here used. In the exogenous root development, the root cap is formed from the outermost cell-layer by its periclinal divisions, so that the growing root primordium does not damage any other tissues except for the suspensor which is attached to the summit of the root cap. In the endogenous root development, the root cap is formed from an inner tissue. The tissue surrounding the root primordium is dissolved, and usually makes a cavity within the plant body. The embryo of Coix lacryma-jobi develops four root primordia endogenously. The mode of development is somewhat different between the first root and the following three roots. The tissue surrounding the first root primordium begins its dissolution in a very late stage, after the differentiation of the root histogens. The dissolution begins at the place near the proximal end of the first root. From here the cavity is extended slowly to the direction of the root apex. In contrast, the tissues surrounding the following three root primordia are dissolved very early, just after the primordial inception, and the dissolution begins at the whole surface of the primordia. However, the above mentioned difference is to be considered as a small variation within the category of the endogenous development. In the mature embryo the four root primordia obtain quite the same form and structure, and are arranged side by side within a common coleorrhiza. Their peculiar parallel arrangement is a result of adaptation to the structure of the very hard spathe. Everybody agrees to consider the second, third and fourth roots as adventitious roots. Then there is no reason to distinguish the first root from the following three. Thus the first root of Coix is proved to be homologous with an adventitious root. The interpretation of the coleorrhiza as an abortive primary root (Paschkov 1951 etc.) is not agreeable at the present situation, because anatomical and histogenetical evidences are lacking. Formation of unicellular hairs can be observed also on the hypocotyls of many other monocotyledons, and is not specific to the roots. A part of Siegert’S (1989) theory was critically discussed concerning the first root of Gramineae , especially on the definition and nature of the hypophysis.