Is gravity a morphological determinant in plants at the cellular level?

It is not yet known whether higher plants, which have evolved in a gravity oriented environment, can reproduce normally or develop via single cells (somatic or zygotic) and pass normally through all phases of development, tissue differentiation and reproduction through consecutive generations at near-zero g. Most published work deals with directional gravitational stimuli (geotropisms) as they operate on the subsequent growth of preformed plant organs that have acquired the ability to perceive and respond to gravity during development at 1 g. But it should be established whether plant development can proceed normally in the weightless state, especially that critical stage in which single cells produce multicellular units leading to embryos with the growing regions of shoot and root which, in turn, give rise to all the tissues of the plant body. We consider here an experiment that tested whether carrot embryos, capable of developing from cultured somatic cells, could do so under conditions of near-weightlessness. Space flight seemed to have no adverse affects on the induction of such embryos or on the initiation of their organs. But there are still reservations which are discussed. Other systems adaptable to the study of embryogenesis and development in space and to resolve the current reservations are described and their place in future space research is indicated.