Experimental Studies on Growth and Sexual Determination in Equisetum Gametophytes

Abstract

The sexual nature of Equisetum gametophytes has been problematic for many years and is still not settled. Hauke (1967) and Duckett (1970) gave good reviews of earlier studies on Equisetum gametophytes. There is now general agreement that some spores grow into small, sparsely plated,' antheridial gametophytes and others into larger, copiously plated, archegonial gametophytes. The latter subsequently produce antheridial lobes, and thus become bisexual (Hauke, 1969; Duckett, 1970, 1972). Antheridial gametophytes are usually shorter-lived than archegonial or bisexual gametophytes. There is a red pigment associated with antheridium formation, either in antheridial gametophytes or in antheridial lobes of bisexual gametophytes (Hauke & Thompson, 1973). LaRoche (1967) disagrees with the interpretation of bisexuality in Equisetum. He believes that the gametophytes are dioecious, and vegetatively propagate a second gametophyte generation, which may differ sexually from the first. Davis (1973) states that sex in Equisetum is environmentally induced and not genetically fixed, and Duckett (1970) more or less concurs. In an attempt to understand sexual determination in Equisetum gametophytes, various workers have grown them in culture under various conditions (Schratz, 1928; Orth, 1934; Wollersheim, 1957a, b; Hauke, 1968, 1969, 1971; Duckett, 1970, 1972; Ram & Chatterjee, 1970; Davis, 1973). LaRoche (1967) studied E. arvense gametophytes grown on various media, with varying pH and other external conditions. His results were expressed in time of development of antheridia, archegonia, and sporophytes, and he never spoke to the relative numbers of one sex or the other. Duckett (1970, 1972) was directly concerned with the percentage of antheridial gametophytes. Using isolated cultures in test tubes, he studied nine different species of Equisetum and the influence of three different media on their sexual development. His cultures were maintained for a year or longer. Ram and Chatterjee (1970), using both isolation cultures and mass cultures, studied the effects of pH, percent agar, yeast extract, chemical growth regulators, crowding, varying sucrose concentrations, and light intensity. They reported results as percent male, female, bisexual, or vegetative. Stephan (1928) apparently was the first to grow Equisetum gametophytes on agar in a defined medium. He was also the first to study the effect of light quality and intensity on Equisetum gametophyte development. Klebs (1917) earlier had studied the effect of blue and red light on fern gametophyte development (see the review of experimental studies on fern gametophytes by Miller, 1968). Orth (1934) used isolation cultures of Equisetum arvense and E. fluviatile to test the effect of a