GENOTYPIC VARIATION AND ALTERNATING DNA LEVELS AT CONSTANT CHROMOSOME-NUMBERS IN THE LIFE-HISTORY OF THE BROWN ALGA HAPLOSPORA-GLOBOSA (TILOPTERIDALES)

The brown algal order Tilopteridales contains three monospecific gener a with reduced life histories, which are assumed to have been derived from ancestors with oogamous reproduction and alternation of generatio ns. The Newfoundland population of Haplospora globosa Kjellman still s hows an alternation of gametophytes and sporophytes, but the chromosom e numbers remain equal because of parthenogenesis and apomeiosis. Howe ver, DNA fluorometry showed that the DNA level is twice as high in the sporophytes as in the gametophytes. The DNA variation at constant chr omosome numbers is presumably due to endomitosis combined with a low d egree of polyteny. A genotypic variant of Haplospora is represented by the population at Helgoland (F. R. G.) where only sporophytes exist. Spores develop into sporophytes instead of gametophytes, and the plant s have a reduced chromosome number but the same DNA level as the Newfo undland sporophytes.