Potassium permanganate fixative and the electron microscopy of sieve tube contents.

Sieve tube "slime" is probably fibrillar as suggested by other workers. The granular material seen in electron micrographs of sieve tubes "fixed" with potassium permanganate is mostly a precipitate produced by the reaction of the permanganate with the sieve tube contents, particularly with sucrose, and with reagents used in the fixing, dehydrating and embedding process. Potassium permanganate is not therefore a good fixative for the electron microscopy of sieve tube contents. Neither is it suitable for the study of fine structure in vacuoles or vesicles containing precipitable solutes in other kinds of cells nor for examining the fine structure of their ground cytoplasm.