LIGHT AND ELECTRON MICROSCOPE OBSERVATIONS ON THE TUBE-DWELLING DIATOM AMPHIPLEURA RUTILANS (TRENTEPOHL) CLEVE

The tubular sheath of Amphipleura rutilans is composed of small fibrils 20–25 A in diameter. The endotubular environment is further partitioned by individual cell sheath formation. The tube boundary seems to be an effective barrier against damage from extreme salinity changes, but does not prevent passage of EDTA, neutral red, surfactants, or caffeine. Terminal swellings develop on growing tips during extremely cold periods. These give rise to 2 or more separate growing tips which proceed to form regular tubes. There was no evidence for sexual reproduction or auxospore formation within the terminal swellings, even though adjacent swellings fused. Bacterial, algal, and fungal epiphytes were abundant on the extratubular surface. Hollow lipid bodies occurred in many cells. A rimring strand of presumed DNA occurs in the chloroplast. It is proposed that the tube material serves not only as a protective boundary but also functions as an active nutrient trap.