Abstract
1. The seeds of Melandrium album were treated with a 0.04% aquaous solution of colchicine, a part of them for 5 days and the rest for 10 days. Five per cent of seedlings from the 5-days and 12.5 per cent from. the 10-days treatment samples were found to be mixoploid consisting of 2X and 4X cells.
2. These mixoploids were mostly sectorial chimerae, so that manner of distributions of the 2X and 4X tissues were various and there were observed, though rarely, very complicated intermingling of those two kinds of cells between rather pure 2X and 4X tissues.
2X-and 4X-flowers are different from each other in their sizes, but not in their shapes, while the shape of the flowers having intermingled cells vas different from those with 2X- or 4X-cells.
Sometimes 2X- and 4X-PMCs appeared intermingled in one and the same sporangium and they behaved themselves as in the non-intermingled sporangium. Regular tetrad formation occurred in those 2X-PMCs, while in the 4X-PMCs the irregular behaviours of the quadrivalents caused the formation of several irregular pollen grains, including sterile ones. These behaviours will be the chief cause of the fact that the di-tetramixoploid plants gave much more 2X-offsprings than 4X or 3X ones.
3. The mixoploidy can not be considered as affecting the length of the juvenile period. The latter is probably due to special genes. The mixoploid plants bloomed a little later than the diploid plants having same kind of genes.
4. The epidermis seems to play a role on the determination of the organs so far as their size is concerned.
Here the writer wishes to express her hearty thanks to Prof. K. Fujii for his kind advise in the course of the investigation. The writer's best thanks are also due to the Japan Society for the Advancement of Cytology by a grant from which this work was made possible.
