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    Accepted: 4 August 1976.

  • The first author (J. R. R.) is very grateful to J. D. Pickett-Heaps, University of Colorado, Boulder, for the use of his laboratory the summer of 1973 during which time most of the CPD preparations were made and studied. We are also indebted to R. McGrew, E. Marchant and K. Gerschenbaum, University of Colorado, and to R. Wibel, University of Illinois, for their technical assistance and helpful discussions. We also acknowledge the helpful discussions with John McClendon, University of Nebraska. This research was supported in part by a University of Nebraska Junior Faculty Research Fellowship awarded to J. R. R.

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The envelope and stalk of Colacium mucronatum Bourr. & Chad, were examined in living cells with light microscopy and in fixed preparations with scanning electron microscopy using critically point dried (CPD) and freeze dried (FD) preparations. The envelope of palmelloid cells is formed over the entire cell surface by many individual strands attached at right angles to areas of articulation of the pellicular strips. Strands were observed to anastomose on the posterior tip of otherwise naked cells. Stalks of living cells in India ink preparations had an optically dark inner core with a lighter outer sheath. In FD stalks a definite inner core was not evident, whereas CPD stalks had an outer surface composed of thick strands which may be the collapsed and aggregated strands of the FD stalks. In both there was also an amorphous matrix. The stalk forms from the aggregation of many strands from the anterior cell tip back to a point encompassing the cell surface anterior to a cross section of the tip 9 μm diam. The outer surface of the stalk comes from the pellicular surface joining that area and the core from the cell tip in the area of the canal opening. Any possible participation of the inner canal surface in stalk formation could not be determined because of the great density of the mucilage at the cell-tip/stalk junction.