AN ULTRASTRUCTURAL STUDY OF PIT CONNECTIONS AND PERCURRENT PROLIFERATIONS IN THE RED ALGA NEMALION HELMINTHOIDES (VELL. IN WITH.) BATT.

Abstract

SUMMARY Nemalion helminthoides exhibits considerable diversity in pit connection morphology. Their diameter ranges from 1.5 μm between fusion cells and the gametophyte, down to 0.3 μm on spermatial branches. Highly asymmetrical pit connections occur in the septa at the base of hairs. The plugs between the vegetative cells of the cortex possess a central groove, but this is absent from those in the medulla and on spermatial branches. The plug cap is three layered except at the base of hairs where only the innermost stratum is present. This last layer also extends as the border to the sides of the plugs separating them from the cell membrane which is continuous between adjacent cells. Granular material occurs in the cytoplasm adjacent to the plug caps, and peripheral to this is a region lacking ribosomes.Up to four successive spermatia and up to twelve hairs may be produced by percurrent proliferations in Nemalion. Absence of pit connections in the walls remaining after spermatium discharge suggests that pit connection displacement may be important in the liberation of the male gametes. Pit connections may also have a mechanical role in anchoring the cytoplasm and providing cross‐bridges between adjacent cells.