A Pair of Compatible Strains of Absidia glauca which has become Heterogamous in Culture

Abstract

A PAIR of compatible (‘plus’ and ‘minus’) strains of the heterothallic mould Absidia glauca which had already been maintained for some years in the culture collection of the Department of Botany of the Imperial College of Science and Technology, London, was first observed by me in the autumn of 1932. At that time the strains, when mated on a suitable medium, produced numerous zygospores of typical form, in other words, the gametangia were equal in size and both suspensors bore the characteristic curved bristles. By 1945 the number of bristles produced by the suspensor cells of the ‘minus’ strain was much fewer than the number produced by the ‘plus’ strain. At the time of writing the ‘minus’ strain produces only small gametangia, the suspensors of which bear few (Fig. 1 c) or no bristles (Fig. 1 a, b, d, e). The zygospores, which are still formed freely, resemble those of the homothallic Absidia spinosa. The conjugating progametangia are unequal in size from an early stage of development (Fig. 1 a). Unfortunately no camera lucida drawings of these strains in the original isogamous condition are available. It is clear, however, that a change from an isogamous condition to a heterogamous one has occurred.