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MANUAL FERTILIZATION AND CHANCE CROSSING - Part 1 |
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Chance fertilization has produced many good roses. The stamens are above the stigma and pollen can fall on to the female organ even before the bloom opens. Self-pollination may also be helped by wind or insects, or cross-pollination may result from insects carrying pollen from one variety to another. However, most of the best roses come from manual crosses.
The best time for artificial cross-pollination is early summer. In spring, roses are in their greatest and best flush of bloom, but atmospheric conditions are subject to variation sufficient to cause failure of the process of fertilization. In autumn, in addition to this same objection, there is often insufficient time for the seed to ripen. Rose flowers in early summer will be part of the second blooming. They will open more readily because of fewer petals than in spring or autumn, and so render fertilization easier. Varieties must be chosen in accordance with the preconceived plan. All crosses may not be possible on the one day, for some of the blooms may not be in a fit condition. Roses open quickest just after sunrise. A bloom of the variety chosen for pollen is selected when about half open. The stamens must not be showing. It can be cut, taken indoors, and kept in water until it opens, or it can be left on the plant. The former is probably the better, since no pollen is lost in wind or taken by bees. If the latter course is chosen the centre petals are removed by fingers or forceps, leaving only the outer two or three rows. The stamens are not touched. The bloom is then covered with butter-muslin eight or ten inches square. This is loosely tied round the flower-stem, and is to protect the pollen, as it ripens during the next hour or two, from pollution by insects with pollen from other roses. Mixing of pollens would destroy all certainty of origin of the male factor in fertilization. A bloom of the variety chosen for seed-bearing is next selected. Like the pollen-parent bloom, it should be about half open. The stamens must not be showing, for then there would already have been a chance of self-fertilization. Here, too, the central petals are removed, exposing the immature stamens and stigma. With a narrow sharp knife or fine forceps the ring of stamens is carefully and completely removed. Injury to the stigma must be avoided. The bloom is covered with butter-muslin in just the same way as that of the pollen parent. Different varieties require different times for the stigma to become receptive for application of pollen. In some, it matures within a few hours, while in others it needs a full day. When receptive, a stigma is sticky, a provision of Nature fox retention of any pollen applied by either accident or intent. Pollen ripens quickly. It becomes floury in appearance and adheres readily to the finger. It is rendered unfit for use if wet, or if dried from long exposure to a hot sun. Successful pollination after midday is rare. Fertilization is most successful between sunrise and about 11 a.m., with no wind and the temperature above 70 degrees Fahrenheit. It can be done in either of two ways. The pollen-bearing bloom can be brought from indoors or be freshly cut from the plant, and the stamens are made to touch lightly the stigma of the prepared bloom. In the other method some pollen is taken from stamens on a fine camel-hair brush and transferred to the stigma. Fertilization does not actually occur until the pollen-grain meets the seed. This takes a few hours after pollination, and so the seed-bloom must be re-covered after pollination to prevent secondary pollination by insects. Such secondary pollination could possibly achieve fertilization before the planned work and so upset all plans. It is advisable to leave the cover in place for several days after pollination. |
