CHLOROPLAST MORPHOLOGY AND FINE STRUCTURE IN BRITISH FUCOIDS

Abstract

Chromatophores, principally from eggs, of representatives of the seven genera of the Fucales found in Britain were investigated with the electron microscope and the results are presented here. The chromatophores are bounded by two pairs of membranes inside which lamellations consisting of three or four non‐cohering thylakoids are embedded in a stroma. The stroma of some genera is extended into a simple projecting, stalked pyrenoid and the inner pair of membranes (chromatophore envelope) loop back on themselves to form a covering also to the pyrenoid. The outer pair of membranes (chromatophore E.R.) take no part. Alternatively, two pyrenoids in close proximity, enclosed by a double looping of the chromatopbore envelope, may be found; they lie one above the other either facing in opposite ways or at right angles to each other. More rarely, two widely separated pyrenoids may be found. Pyrenoids of this sort do not occur in association with the egg chromatophores in the Fucaceae (Fucus, Ascophyllum and Pelvetia), but they do occur in the eggs (but not in thallus cells) of members of the Cystoseiraceae (Bifurcaria and Cystoseira), with the exception of Halidrys, and in the Himanthaliaceae (Himanthalia). These pyrenoids are regarded as rudimentary, and as representing a stage close to total eclipse. Pyrenoids in such a natural group are suggested to have phyletic value, their presence being thought to be indicative of greater antiquity than their absence. Hence members of the Fucaceae are thought to be more specialized than members of the Cystoseiraceae. This statement is discussed in relation to earlier results (Manton, 1964, etc.) where the Cystoseiraceae were found to have other kinds of primitive features, and the Fucaceae other kinds of advanced features. Copyright © 1968, Wiley Blackwell. All rights reserved