Recent studies suggest that the membrane system in embryonic tissue may be the primary structure which is affected by adverse environmental conditions occurring during imbibition and germination. Therefore, elucidating the fine-structure of membranes in radicle meristems of dry seeds and observing changes that occur during germination under normal and adverse conditions could help to explain how environmental stress affects embryonic tissue. To address this question, a preliminary study was undertaken to examine the membrane system in dry seeds (11% moisture) of cotton. Scanning and transmission electron microscopy were used to examine cryofractured tissue, thin sections and freeze fractured replicas of embryonic tissue that had been prepared either from fresh, chemically fixed or cryoprotected material. Observations of the material reveal that a typical radicle cell has a nucleus and a sparse population of mitochondria and proplastids each surrounded by an intact double membrane or envelope.In addition, the cell contains cisternae of the endoplasmic reticulum and protein bodies, both being limited by single membranes. The most numerous organelles in the cells are lipid bodies which are bounded by a single electron dense structure about 2 nm wide. The lipid bodies exhibit two close physical relationships: they surround the protein bodies and they are appressed to the inner surface of the plasmalemma. These observations of the embryonic cells indicate that the structural continuity of all membranes is preserved in the dry seeds. Furthermore, their fire-structure does not differ significantly from that exhibited in hydrated plant cells, i.e. all membranes have a unit membrane structure which is characteristic of those with a phospholipid bilayer. These conclusions do not support the observations of others who have indicated that embryonic tissues withlow moisture contents exhibit membrane disorganization and discontinuity. In addition, our results do not support a recent model which proposes that membrane phospholipids in tissues containing less than 20% water moisture form hexagonal arrays which effectively provide "pores" that could account for free diffusion of ions and solutes during imbibition. If indeed membrane pores are formed in dry tissues, their detection is beyond the limit of resolution for the techniques which we used. The preponderance of lipid and protein bodies and the physical relationships that they exhibit, suggest that these organelles represent storage products that are readily available for membrane biogenesis during imbibition and germination. Further investigations in our laboratory will pursue this possibility.