Embryogenic cell lines with lasting embryogenic potential can be obtai
ned from somatic embryos induced directly from zygotic embryos of Arab
idopsis thaliana, ecotype Columbia. The response to a critical concent
ration of auxin, which seems to be the all-important factor in the gen
eration of embryogenic cell lines, is exhibited by somatic embryos but
not by zygotic ones. The basis for this differential response remains
obscure and will be discussed in relation to other systems.