(5/11. See Mr. W. Earley in 'Nature' 1872 page 242, to the same effect. He once, however, saw bees visiting the flowers, and supposed that on this occasion they would have been intercrossed.) I have myself purposely made similar trials with the same result. Although the varieties always come true, yet, as we shall presently see, one of the five well-known varieties occasionally gives birth to another, which exhibits all its usual characters. Owing to this curious fact, and to the darker-coloured varieties being the most productive, these increase, to the exclusion of the others, as I was informed by the late Mr. Masters, if there be no selection.
In order to ascertain what would be the effect of crossing two varieties, some flowers on the Purple sweet-pea, which has a dark reddish-purple standard-petal with violet-coloured wing-petals and keel, were castrated whilst very young, and were fertilised with pollen of the Painted Lady. This latter variety has a pale cherry-coloured standard, with almost white wings and keel. On two occasions I raised from a flower thus crossed plants perfectly resembling both parent-forms; but the greater number resembled the paternal variety. So perfect was the resemblance, that I should have suspected some mistake in the label, had not the plants, which were at first identical in appearance with the father or Painted Lady, later in the season produced flowers blotched and streaked with dark purple. This is an interesting example of partial reversion in the same individual plant as it grows older. The purple-flowered plants were thrown away, as they might possibly have been the product of the accidental self-fertilisation of the mother-plant, owing to the castration not having been effectual. But the plants which resembled in the colour of their flowers the paternal variety or Painted Lady were preserved, and their seeds saved. Next summer many plants were raised from these seeds, and they generally resembled their grandfather the Painted Lady, but most of them had their wing-petals streaked and stained with dark pink; and a few had pale purple wings with the standard of a darker crimson than is natural to the Painted Lady, so that they formed a new sub-variety. Amongst these plants a single one appeared having purple flowers like those of the grandmother, but with the petals slightly streaked with a paler tint: this was thrown away. Seeds were again saved from the foregoing plants, and the seedlings thus raised still resembled the Painted Lady, or great-grandfather; but they now varied much, the standard petal varying from pale to dark red, in a few instances with blotches of white; and the wing-petals varied from nearly white to purple, the keel being in all nearly white.
As no variability of this kind can be detected in plants raised from seeds, the parents of which have grown during many successive generations in close proximity, we may infer that they cannot have intercrossed. What does occasionally occur is that in a row of plants raised from seeds of one variety, another variety true of its kind appears; for instance, in a long row of Scarlets (the seeds of which had been carefully gathered from Scarlets for the sake of this experiment) two Purples and one Painted Lady appeared. Seeds from these three aberrant plants were saved and sown in separate beds. The seedlings from both the Purples were chiefly Purples, but with some Painted Ladies and some Scarlets. The seedlings from the aberrant Painted Lady were chiefly Painted Ladies with some Scarlets. Each variety, whatever its parentage may have been, retained all its characters perfect, and there was no streaking or blotching of the colours, as in the foregoing plants of crossed origin. Another variety, however, is often sold, which is striped and blotched with dark purple; and this is probably of crossed origin, for I found, as well as Mr. Masters, that it did not transmit its characters at all truly.
From the evidence now given, we may conclude that the varieties of the sweet-pea rarely or never intercross in this country; and this is a highly remarkable fact, considering, firstly, the general structure of the flowers; secondly, the large quantity of pollen produced, far more than is requisite for self-fertilisation; and thirdly, the occasional visit of insects.