As these matters are all treated of under their respective headings, it is not necessary to allude to them again in detail. It may be well, however, to allude, in general terms, to the causes which have been assigned by various writers for their formation, and to the means which have been adopted by practical experimenters to secure the production of the flowers often so much esteemed by the florist. It must be admitted that, in spite of all that has been written on the subject, but very little is known about these matters. In the case of the stock the following means have been adopted by cultivators in order to obtain plants bearing double instead of single flowers. There is first the crossing of single flowers with double ones, effected by planting a double-flowered plant in proximity to a single-flowered one; but this, it is obvious, could lead to no important results, since the double flowers, having no pollen, could not possibly influence the seed, which is borne only by the single-flowered plants. Another plan is the degustation of the buds, that is to say, the chewing of the well-formed buds; it is held that the single plants can be recognised by their sweeter taste and greater consistence, and may thus be weeded out; but there is at least the disadvantage attending this method, that the plants, single as well as double, must all be grown up to the period when these buds are tolerably well advanced. A third method which has been adopted is, that of sowing the seeds at a particular lunar epoch, great confidence being placed in the plan of planting them during the last quarter of the moon, but such confidence is found to be misplaced. The plan of removing the stamens has had its supporters, but as this must be done at an early stage of development, and could only influence the result by diverting the vital force which would be expended in the maturation of the pollen, to the perfecting of the seeds, it is obvious that the plan is impracticable for all ordinary purposes, even if in any degree efficient, which from the plasticity of vegetable development, and the faculty of doubling which is inherent in the stock family, is not at all improbable. Still another mark, the presence of a fifth petal in the single or seed-bearing flower, has been held to indicate the assurance of obtaining a crop of double-flowered plants from seeds saved from flowers possessing this peculiarity. To a certain extent, doubtless, this expectation would be realised, owing to the plasticity and inherent quality just alluded to, but the proportion would be too small for any useful practical purpose.
"The gardeners of Erfurt," observes M. Chaté, who has written a book[565] on the subject, in which he makes known a means of obtaining double-flowered stocks founded on more than fifty years' practice in his family, "have, for a long time, to a certain extent monopolised the sale of seeds of these plants. To obtain these seeds, the Erfurt gardeners cultivate the flowers in pots, and place them on shelves in large greenhouses, giving them only sufficient water to prevent them from dying. So cultivated the plants become weakened, the pods shortened, and the seeds less numerous, and better ripened; and these seeds give from 60 to 70 per cent. of double flowers.
"The seeds from these plants are said to be mostly of an abnormal shape, which is so striking that experienced cultivators are able to separate those which would furnish double flowers from those which would produce single ones."
M. Chaté's method, which he calls the French one, gives still greater results, viz.: 80 per cent. of double flowers, and these produced by very simple means. "When my seeds," he observes, "have been chosen with care, I plant them, in the month of April, in good dry mould, in a position exposed to the morning sun, this position being the most favourable. At the time of flowering I nip off some of the flowering branches, and leave only ten or twelve pods on the secondary branches, taking care to remove all the small weak branches which shoot at this time. I leave none but the principal and the secondary branches to bear the pods. All the sap is employed in nourishing the seeds thus borne, which give a result of 80 per cent. of double flowers. The pods under this management are thicker, and their maturation is more perfect. At the time of extracting the seeds the upper portion of the pod is separated and placed aside, because it has been ascertained that the plants coming from the seeds situated in this portion of the pod, give 80 per cent. of single flowers. They yield, however, greater variety than the others. This plan of suppressing that part of the pod which yields single flowers in the largest proportion, greatly facilitates the recognition of the single-flowered plants, because there remains to be eliminated from among the seedlings only from 10 to 15 per cent.
This separation of the single from the double-flowered plants, M. Chaté tells us is not so difficult as might be supposed. The single stocks, he explains, have deep green leaves (glabrous in certain species), rounded at the top, the heart being in the form of a shuttlecock, and the plant stout and thickset in its general aspect, while the plants yielding double flowers have very long leaves of a light green colour, hairy, and curled at the edges, the heart consisting of whitish leaves, curved so that they enclose it completely. Such is the substance of M. Chaté's method of securing so large a proportion of double-flowered plants, and then of separating them from the remaining single ones—a method which commends itself to the good sense of the intelligent cultivator."[566]
Signor Rigamonti, a great cultivator of pinks, asserted that he was able to distinguish double from single-flowered pinks, in the seedling state. According to this gentleman, those seedlings which produce three cotyledons in a whorl in place of two, form double flowers. In the case of Primula sinensis the same results occurred. Some had three leaves in a ring, others two; most had the leaves standing one over the other as usual. These were divided into three sets, and when they flowered, the first lot were all double, the second semi-double, the third single. But these statements have not been confirmed by other observers; and the writer can safely assert that seedling pinks occasionally produce three cotyledons, and subsequently single flowers. He has never observed a double flower under these circumstances, though it is true his experience in this matter has been but small.
A writer in Otto's 'Gartenzeitung,' considers that double flowers are a consequence of dryness of soil and atmosphere, and not of a luxurious soil, rich in nutritious matter, having arrived at this conclusion from an observation of the following circumstances:
"Fifty years ago we saw Kerria japonica in a hothouse with single flowers. Twenty years later we met with it in several gardens, in the open air, but always with double flowers. At this time we were assured that single-flowered plants were no more to be found in the whole of Europe, and botanists forming herbaria offered considerable sums for a branch of K. japonica with single flowers. We were requested to take the plant in hand for the purpose of inducing it to produce single flowers. We were advised to plant it out in a rich soil, which was done, but, by chance, the situation was sloping, consequently it did not retain moisture, and all the flowers produced for several years in succession were double. Shortly after, the captain of an English ship again brought plants bearing normal flowers from Japan, which were soon spread over the continent, and of which we received one plant. After three years all the young plants raised from cuttings were double-flowered.
"In the year 1820 we several times visited a garden in the neighbourhood of Vienna, well known on account of its plant culture. The gardener there possessed an immense plant of Camellia japonica with single flowers, and some small plants raised from this by cuttings, but no other variety of camellia. He fertilised the flowers with their own pollen, harvested seeds, which he sowed, and the plants raised from them were placed in an extremely dry, lofty conservatory, where, after some years, instead of producing single flowers, they all produced double ones. The seedlings and mother plant were planted in one and the same kind of earth, and some of the flowers on the old plant also showed an inclination to become double.