UNIFORM COLOUR OF THE FLOWERS ON PLANTS, SELF-FERTILISED AND GROWN UNDER SIMILAR CONDITIONS FOR SEVERAL GENERATIONS.
At the commencement of my experiments, the parent-plants of Mimulus luteus, Ipomoea purpurea, Dianthus caryophyllus, and Petunia violacea, raised from purchased seeds, varied greatly in the colour of their flowers. This occurs with many plants which have been long cultivated as an ornament for the flower-garden, and which have been propagated by seeds. The colour of the flowers was a point to which I did not at first in the least attend, and no selection whatever was practised. Nevertheless, the flowers produced by the self-fertilised plants of the above four species became absolutely uniform in tint, or very nearly so, after they had been grown for some generations under closely similar conditions. The intercrossed plants, which were more or less closely inter-related in the later generations, and which had been likewise cultivated all the time under similar conditions, became more uniform in the colour of their flowers than were the original parent-plants, but much less so than the self-fertilised plants. When self-fertilised plants of one of the later generations were crossed with a fresh stock, and seedlings thus raised, these presented a wonderful contrast in the diversified tints of their flowers compared with those of the self-fertilised seedlings. As such cases of flowers becoming uniformly coloured without any aid from selection seem to me curious, I will give a full abstract of my observations.
Mimulus luteus.
A tall variety, bearing large, almost white flowers blotched with crimson, appeared amongst the intercrossed and self-fertilised plants of the third and fourth generations. This variety increased so rapidly, that in the sixth generation of self-fertilised plants every single one consisted of it. So it was with all the many plants which were raised, up to the last or ninth self-fertilised generation. Although this variety first appeared amongst the intercrossed plants, yet from their offspring being intercrossed in each succeeding generation, it never prevailed amongst them; and the flowers on the several intercrossed plants of the ninth generation differed considerably in colour. On the other hand, the uniformity in colour of the flowers on the plants of all the later self-fertilised generations was quite surprising; on a casual inspection they might have been said to be quite alike, but the crimson blotches were not of exactly the same shape, or in exactly the same position. Both my gardener and myself believe that this variety did not appear amongst the parent-plants, raised from purchased seeds, but from its appearance amongst both the crossed and self-fertilised plants of the third and fourth generations; and from what I have seen of the variation of this species on other occasions, it is probable that it would occasionally appear under any circumstances. We learn, however, from the present case that under the peculiar conditions to which my plants were subjected, this particular variety, remarkable for its colouring, largeness of the corolla, and increased height of the whole plant, prevailed in the sixth and all the succeeding self-fertilised generations to the complete exclusion of every other variety.
Ipomoea purpurea.
My attention was first drawn to the present subject by observing that the flowers on all the plants of the seventh self-fertilised generation were of a uniform, remarkably rich, dark purple tint. The many plants which were raised during the three succeeding generations, up to the last or tenth, all produced flowers coloured in the same manner. They were absolutely uniform in tint, like those of a constant species living in a state of nature; and the self-fertilised plants might have been distinguished with certainty, as my gardener remarked, without the aid of labels, from the intercrossed plants of the later generations. These, however, had more uniformly coloured flowers than those which were first raised from the purchased seeds.