actually found by experiment. It will be noticed that in the whole family the purples are to the reds as 3 : 1, and the longs are also three times as numerous as the rounds. The peculiarity of the case lies in the distribution of these two characters with regard to one another. In some way or other the factors for blue and for long pollen become linked together in the cell divisions that give rise to the gametes, but the linking is not complete. This holds good for all the four cases in which repulsion between the factors occurs when one of the two factors is introduced by each of the parents. _When both of the factors are brought into the cross by the same parent we get coupling between them instead of repulsion._ The phenomena of repulsion and coupling between separate factors are intimately related, though hitherto we have not been able to suggest why this should be so. Nor for the present can we suggest why certain factors should be linked together in the peculiar way that we have reason to suppose that they are during the process of the formation of the gametes. Nevertheless the phenomena are very definite, and it is not unlikely that a further study of them may throw important light on the architecture of the living cell. APPENDIX TO CHAPTER IX As it is possible that some readers may care, in spite of its complexity, to enter rather more fully into the peculiar phenomenon {96} of the coupling of characters, I have brought together some further data in this Appendix. In the case we have already considered, where the factors for blue colour and long pollen are concerned, we have been led to suppose that the gametes produced by the heterozygous plant are of the nature 7 BL : 1 Bl : 1 bL : 7 bl. Such a series of ovules fertilised by a similar series of pollen grains will give a generation of the following composition:-- 49 BBLL + 7 BBLl + 7 BbLL + 49 BbLl + 7 BBLl + 7 BbLL + BbLl + BbLl + 49 BbLl \---------------------------------/ 177 purple, long + BBll + 7 Bbll + bbLL + 7 bbLl + 49 bbll + 7 Bbll + 7 bbLl \-------------/ \-----------/ \-----/ 15 purple, 15 red, 49 red, round long round