Contributions to the Karyology of the Ulotrichales — I. Ulothrix

¹ Part of the work approved for the award of the Ph. D. degree by the University of London in 1958.

Abstract

The karyology of Ulothrix zonata and U. subtilissima is described. Their chromosome numbers are 10 and 14, respectively. Earlier findings of Schussnig on U. zonata as regards the chromosome number, the occurrence of nucleolar granules, “polar” granules, and the continuity of the nucleolus from interphase to interphase are not borne out by the present investigation. Mitotic divisions were found to be normal. The chromosomes of U. zonata were observed to be the largest amongst the Ulotrichales investigated by the author, while those of U. subtilissima are small and dot-like. The orientation of the chromosomes during anaphase in U. zonata suggests that they possess presumably subterminal centromeres. Some of the chromosomes of this species have conspicuously nonstaining regions which are probably heterochromatic. Divisions during swarmer formation, which are largely successive, are all mitotic, revealing the same chromosome number as in vegetative filaments.