SYSTEMATIC SIGNIFICANCE OF THE ABSENCE OF PIT‐PLUG CAP MEMBRANES IN THE BATRACHOSPERMALES (RHODOPHYTA)1

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Abstract
Four species of the Batrachospermales were examined by transmission electron microscopy to determine whether or not cap membranes, a typical structural component of pit plugs in several orders of red algae, were present. Routine specimen preservation methods used in past studies led to contradictory reports, soBatrachospermum keratophytumBory,B. sirodotiiSkuja ex Reis,Sirodotia suecicaKylin, andS. tenuissima(Collins) Skuja ex Flint were prepared by secondary fixation in potassium permanganate or a combination of potassium ferrocyanide‐osmium tetroxide to enhance membrane contrast. These fixation procedures produced clear, well‐contrasted images in which cap membranes were absent. The absence of cap membranes inS. suecicaandS. tenuissimaand the presence of cap membranes in two members of the Nemaliales was confirmed by freeze‐substitution methods. Absence of cap membranes in representatives of the Batrachospermales further distinguishes the Batrachospermales from the Nemaliales, the order in which they long resided, and demonstrates the value of this character in elucidating ordinal alliances among the Rhodophyta.