The Argonne Laboratory has designed and developed a 4-pi, or omnidirectional, clinostat. By rotating a plant so that the force of gravity is distributed evenly over all possible directions, the directional effects of gravity are eliminated, simulating some aspects of the zero-g state. It was shown that certain plants grew more slowly and had fewer and smaller leaves, while others had about 25 percent greater replication of fronds and had greater elongation of certain plant parts. It will be extremely interesting to compare these effects under zero-g conditions in orbiting spacecraft. The effect of gravity in transporting growth hormones in plants has been demonstrated at Dartmouth College using radiocarbon-labeled growth hormones. Plant geotropisms and growth movements have been studied and biosatellite experiments developed. Anatomy is considered a derivative adaptation to gravity ([ref.67]). A large background of plant research exists on the effect of orientation on plant responses. Information from clinostat experiments is considered susceptible of extrapolation to low gravity conditions because the threshold period for gravitational triggering is relatively long. Once over critical minimum dimensions, the major effects of low gravity would be assumed to occur in those heterocellular organisms that develop in more or less fixed orientation with respect to terrestrial gravity and which respond to changes in orientation with relatively long induction periods; these are the higher plant orders. On the other extreme are the complex primates which respond rapidly, but whose multiplicity of organs and correlative mechanisms are susceptible to malfunction and disorganization. It may be suggested that the heterocellular lower plants and invertebrates will be less affected. Perturbations of the environment to which the experimental organism is exposed must be limited or controlled to reduce uncertainties in interpretation of the results. At the same time, the introduction of known perturbations may assist in isolating the effects due solely to gravity. Study of _de novo_ differentiation and other phenomena immediately after syngamy may be of particular importance. Study of anatomical changes after exposure of the organism to low gravity is important. BIOLOGICAL EFFECTS OF SPACE RADIATION¹ ¹ This section includes part of the Summary of the Panel on Radiation Biology of the Environmental Biology Committee Space Science Board, NAS/NRC (1963), and results of research by the Bioscience Programs, NASA. Radiation sources in space are of three types: galactic cosmic radiation, Van Allen belts, and solar flares with an intense proton flux. Cosmic radiation has higher energy levels than radiation produced by manmade accelerators.