Translocation in the Stolon of Saxifraga sarmentosa L. The Ultrastructural Background

The ultrastructure of the mature sieve elements of the Saxifragastolon is described. Theseare narrow (3–5 µm) andfairly long (100-300 µm). The sieve plate pores were invariablyfound to be closely-occluded with P-protein. It is argued thatthe double-cutting technique used for excision invalidates thecontention that this must be interpreted as an artifact. TheP-protein filaments appear to consist of a double helix. Stereomicrographs at normal voltages, and at 1 MV in the AEI-EM₇ microscopeare presented.