The egg, zygote, and young embryo of cotton possess a tube-containing ER. The tubes are 290-310 Å in diameter, microns in length, crooked, and branched. They are preserved with either GaOs or KMnO4. The ER within which they occur has attached ribosomes. The membrane of the ER and the membrane of the tubes is continuous at the ends, thus the interior of the tubes is open to the ground cytoplasm. The origin of the tubes is not clear, but they appear to be unrelated to the microtubules found in the cytoplasm of the cell. They are postulated as having a role in the reduction of cell volume during the development of the zygote. © 1968 Academic Press Inc.
