W. J. Borsje’s research while affiliated with Vrije Universiteit Amsterdam and other places

The morphology of two species of Acrochaetium, provisionally identified as A. polyblastum (Rosenv.) Børg. and A. hallandicum (Kylin) Hamel, is described in some detail. They are shown to be tetrasporophyte and gametophyte respectively in the same life history. Both phases are characterized by the possession of a stellate chromatophore with a central pyrenoid; the tetrasporophyte has a spore which germinates septately and subsequently develops a multicellular filamentous base, the gametophyte has a unicellular base.The sexual cycle is mainly temperature-controlled, the gametangia being formed under higher temperature than the tetrasporangia. Both generations reproduce asexually by means of monospores, in a wide temperature range.The morphological variability, as affected by different environmental conditions, appears to be very large; moreover there is an ample variation between different clones grown under uniform conditions. General structure of the plant, the type of spore germination in each phase, and cell diameter are the most reliable characters in delimiting the species from other acrochaetioid taxa.The life histories of Acrochaetium species possessing stellate chromatophores, as exemplified by a number of different species now, show a remarkably uniform pattern, as far as alternation of morphological phases is concerned. It is suggested that characters of the total life history provide a reasonable basis for the systematics of the acrochaetioid algae.

The morphology of Acrochaetium dasyae Collins is described in detail from material collected along the Dutch coast. This material consists of predominantly unisexual gametophytes with a prominent persistent basal spore and a multicellular filamentous prostrate system, which may be more or less endophytic in Dasya pedicellata (C. Ag.) C. Ag.. Some additional remarks are made on field-collected specimens of A. dasyae from Swedish and Eastern-Canadian coasts. The life-history was completed in culture and turned out to be a diplobiontic cycle consisting of slightly heteromorphic generations. Gametophyte and tetrasporophyte differ in persistence or non-persistence of the basal spore, and to a lesser degree in morphology of the basal system and arrangement of the monosporangia.Material presumably representing the tetrasporophyte was found in two Dutch and several Canadian samples and provisionally identified as Audouinella saviana (Menegh.) Woelkerling; it occurs as an epiphyte on several macroalgae and on Zostera sp..No decision could yet be made concerning the possible conspecificity of A. dasyae with several other species, described either as gametophytes or tetrasporophytes.

1. A short survey of the experimental approach of morphological variability and life cycles of algae is given. 2. The taxonomical implications of experimental investigations is illustrated with respect to some multi-cellular blue-green, red, brown and green algae.