Propagation of Bulbous Plants.
Perhaps there is no one class of plants that have so many ways of being easily increased as bulbous plants proper. Some kinds, e.g., Liliums, Alliums, may be increased in four different ways—from offsets and "spawn," scales, bulbils, and, last of all, seeds.
Offsets.—The great mass of bulbous and cormous plants, however, are so readily multiplied by detaching the offsets from the parent bulb or corm, that the other methods are rarely employed except by trade growers. Nearly all hardy bulbous plants produce offsets freely. These offsets represent a superabundance of nourishment that has been elaborated in the leaves, and very often there are several smaller ones attached to the base of the larger ones that have been produced in precisely the same way.
In the case of Daffodils, Tulips, Hyacinths, Crocuses, Gladiolus, and a host of others, the new offsets are pressed against the sides or on top of the older ones. In the drawing of the Tulip (p. 30), three new bulbs are to be seen surrounding all that is left of the old bulb. This latter has practically vanished up the main axis from the disc to produce flowers and leaves—hence it follows that the Tulip bulb somewhat resembles the corm in its vegetative characters. The bulbs taken out of the soil in early summer are not those that were planted the previous autumn.
Besides "offsets," some plants produce numerous small vegetative bodies called "cloves" or "spawn." These are shown in the drawing of the Gladiolus (p. 14), where two strong flowering corms have been developed on top of the old shrivelled one. At the base of each of these are numerous small outgrowths among the contractile roots. If these growths or spawn are taken off and stored in sandy soil until spring, they may then be planted in special beds, and in the course of two or three years will reach the flowering size.
The Liliums are a large and interesting group of bulbous plants. Many of them produce offsets freely round the base of the old bulb. There are several species, however (e.g., canadense, Grayi, maritimum, pardalinum, Parryi, superbum), which have creeping rootstocks or rhizomes, and the new offsets are produced along these at intervals as shown in the drawing.
Division.—Bulbs or corms are rarely cut up for purposes of propagation. The best example in which this method of increase is practised is the Gladiolus. The larger corms, if they show two or more crown-growths, may be carefully cut down between them with a sharp knife. The cut surfaces may be dipped in soot, not only to dry it more rapidly, but also to prevent any stray spores of fungoid diseases from germinating.
Leaf-Scales.—The thick, fleshy, deltoid scales of many of the Liliums will develop buds at the base, as shown in the drawing, when detached and inserted almost vertically in sandy soil. In about three or four years flowering bulbs can be produced by this means.
A somewhat analogous process is adopted with Hyacinths. The old bulb is slashed across the base of the disc two or three times into the fleshy scales. The cut surfaces dry up, and by-and-bye small buds or bulblets, as shown on the sketch of the Lily scale, make their appearance. In due course these bulblets are detached and planted in light sandy soil. The propagation of the florists' varieties of Hyacinths by this means is not altogether satisfactory, as the old bulbs themselves undergo a deterioration in our variable climate.
Scale leaf (s. l.) of Lily bulb showing new growth (n. b.) at base.
PLATE 9.
Bulbils.—These are vegetative growths—neither seeds, bulbs, nor offsets—that appear in the axils of the aërial leaves, as shown in the sketch. Many Liliums, like bulbiferum, tigrinum, speciosum, Leichtlini, and some of the Alliums produce them with great regularity. It is thought that bulbils are borne by some plants and not others, because the conditions for the fertilisation or ripening of the seeds are not favourable. In such cases, therefore, Nature has provided such plants with this means of reproduction by bulbils, rather than allow them to run the risk of dying out altogether. In Kerner and Oliver's "Natural History of Plants" it is stated that "There are two forms of Orange Lily indigenous to Europe. One (Lilium croceum), occurring especially in the Pyrenees and South of France, almost always ripens fruits and forms no bulbils in its leaf-axils. The other (Lilium bulbiferum), found in the valleys of the Central and Northern Alps, hardly ever fruits, but is characterised by the bulbils it produces in the axils of its leaves; bulbils which disarticulate in autumn and are scattered by the wind. But there is no difference noticeable in the structure of the flowers in these two Orange Lilies, and it is difficult to explain their difference in mode of propagation, save on the assumption that in the regions where Lilium bulbiferum grows those insects are wanting which should convey its pollen from flower to flower. As the Orange Lily possesses no arrangements for autogamy (i.e., self-fertilisation), no fruits are formed in the absence of insect visits. It appears that this plant has lost the capacity for autogamy; at any rate, if a stigma be pollinated with pollen from the same flower on plants in a garden, no result follows. On the other hand, offshoots in the form of numerous bulbils are produced by Lilium bulbiferum, by means of which it is propagated and dispersed. In several valleys of the Central Alps it does not flower at all, and thus obviously depends entirely upon its bulbils for propagation."
The bulbils should not be detached from the stems until the latter are quite ripe, and the foliage shows signs of withering. They may be sown as if they were large seeds. They possess the advantage over seeds, however, inasmuch as they produce flowering bulbs two or three seasons before the bulbs from real seeds come to maturity.
Bulbous Plants from Seeds.—The would-be raiser of bulbous plants from seeds must be gifted with a good deal of patience, and be systematic in his methods, otherwise he will find it is no sinecure to wait from five to ten years before a flower appears from the seeds he sowed at the beginning of those periods. Even when the blossoms do appear, the great majority of them are likely to be inferior in almost every way to their progenitors. The raising of bulbous plants from seeds, therefore, is not likely to find many enthusiastic disciples among amateur growers, who, as a rule, are content to cultivate the varieties that have been evolved by generations of gardeners. Under these circumstances it is most fortunate that bulbous plants can be so readily multiplied by offsets. Of course, in large gardens and nurseries, where there is a trained staff of men, it is a comparatively easy matter to save and sow a certain quantity of seeds each year. After the first period of waiting is over, each season sees a fresh lot of seedlings burst into blossom. Any particularly fine forms are marked, and afterwards increased by means of the offsets or bulbils.
The annexed drawing shows a seedling Tulip. The germination is very similar to that of the common garden Onion. The swollen portion at the base represents the first stage in the development of the bulb, and each year for six or seven seasons sees it increase in size, and ultimately large and strong enough to blossom.
Sowing Seeds.—The seeds of all the perfectly hardy bulbous plants may be sown in the open air, in beds specially prepared for the purpose. The soil should be a light sandy loam with a good sprinkling of leaf-mould in it. The "drills" may be drawn about one inch deep, and as the seedlings in many cases are left to look after themselves until they bloom, the seeds should be sown very thinly—two or three inches apart—so as to allow for future development. It would scarcely be wise, in the case of choice or rare varieties, to trust the seeds to the open air. They may, however, be sown in pots or pans, and after two or three seasons' growth they will be large enough for transferring to the open air. The seeds of bulbous plants may be sown in spring if they ripen late in the year; or in early autumn if they ripen in summer.