Multiplication in vitro de quelques iris à partir de raciness: aspects histologiques de l'embryogenèse somatique

A histo-morphological investigation of indirect somatic embryogenesis was conducted on three species of Iris. The formation of "calli I" or propagules appears somewhat like a root ramification. It is initiated in the pericycle, facing one of the xylem bundles. Fully developed, this so-called callus I differs from a rootlet by its size as well as by the complete absence of an apical meristem and the quasi absence of a root cap. In terms of external and internal structures, it is different from the typical callus of other plants as well as the callus II of Iris. The latter becomes granular on the surface and is internally parenchymatous. This type of callus has an irregular growth that suggests unequal activity of a lateral meristem. This meristem is covered by a discontinuous plectenchyma or pseudoparenchyma of variable thickness that is cytologically heterogeneous. Most of the initial cells of somatic proembryos and embryoids develop in this pseudoparenchyma, of which some fragments remain attached to the embryoids until their development is complete. Key words : Iris, roots, micropropagation, indirect somatic embryogenesis, histology.