IN the Croonian lecture (Proc. Roy. Soc., B, vol. xci., p. 368) I said that the prothallia of a variegated Adiantum were entirely green, though the ferns which arise from them may be green, or variegated, or white. This statement should be corrected, for I find that though the prothallia look all green when growing on the soil, some of them have lighter, occasionally almost white, patches, which are seen as soon as the prothallia are examined by transmitted light. These patches of cells are sharply defined, usually forming radiating bands widening peripherally. In some cases the light tissue is an island of cells entirely surrounded by the green cells. The plastids in the light cells are at least as numerous as those of the green cells, but they are smaller and pale in colour, being mostly a faint green, though sometimes almost colourless. The development of this kind of variegation will need careful study. It is difficult to avoid the inference that genetic segregation does here occur in haploid tissue, but the process is not necessarily postponed, as I suggested, to the formation of the germ-cells.