Report of the Third International Conference on Genetics, 1906. p. 438-445
Hybrids and Hybridisation among Bulbous Plants
C. G. van Tubergen, Junr., of Haarlem, Holland

OF the exceedingly numerous varieties of bulbous plants now grown in Holland and elsewhere in such amazing numbers, all, with very few exceptions, owe their original existence to having been raised from seed. It appears however that, with the exception of the modern raisers of the Daffodil, very few attempts indeed have been made by the general cultivators to do any artificial crossing, or, if any such has been done, to keep a record of it. Whether rightly or not, to me it has always appeared that however beautiful an artificially raised hybrid plant may be, it loses a part of its interest if the parents are unknown. The following is an enumeration of some of the hybrids among bulbous and tuberous rooted plants which have been raised in our nurseries, with brief notes of anything that struck me as being worth noticing:

Fig. 118.—Lilium x Mar-Han (L. martagon album x L. Hansoni).

LILIUM.— Very numerous crosses among various species have been effected, and many seedlings are still under observation; a good and noteworthy race has sprung from the crossing of Lilium Martagon album with L. Hansoni. It is of particular interest to note that whereas L. Martagon album, if raised from seed, almost always comes perfectly true, scarcely ten among a thousand plants reverting to the typical purple Martagon Lily; out of the mingling of L. Martagon album with L. Hansoni not a single white martagon occurred. All plants (several hundreds) that showed no influence of the pollen-parent (L. Hansoni) reverted to the typical purple Martagon Lily. Those that showed the influence of L. Hansoni developed into stately, tall-growing lilies with broad, dark green foliage in whorls and pyramidal spikes, composed of very numerous flowers. The ground colour of the flowers of these hybrids is a more or less pronounced pale buff-brown, either flushed with crimson or with deep orange, and with purple spots. The individual size of the flowers much exceeds that of either parent. I named this strain L. Mar-Han (fig. 118), and I have already distributed two or three distinct varieties of it, while others are still in course of propagation. As far as I know, the cross effected by Mr. Powell of Southborough between L. Martagon dalmaticum and L. Hansoni either produced true hybrids or gave dalmaticum purê. Other crosses which gave good results were effected between L. pardalinum and L. Parryi and also between L. pardalinum and Humboldtii. These, however, have lately been raised also in America.

BRUNSVIGIA JOSEPHINAE.— This remarkable plant freely flowers with me, and I several times fertilised it with pollen of Amaryllis Belladonna. I have now large bulbs, four to six inches across, of these hybrids, which so far have not yet flowered, although some are over ten years old. It is very remarkable that the plants, though raised from seed of the Brunsvigia, show no influence of the mother parent, the bulb and foliage being that of an Amaryllis Belladonna.

COLCHICUM.— Some very interesting plants came out of a cross between C. Sibthorpii and the double white-flowered form of C. autumnale. The seedlings either produced a large, broad-petaled form of C. Sibthorpii or gave perfectly double-flowered C. Sibthorpii, the flowers being composed of hundreds of narrow petals of a lilac-red, faintly chequered with white. These double flowers are perfectly sterile, whereas in the double white-flowered C. antumnale one occasionally finds a good pistil with potent pollen.

EREMURUS.— Some very strong-growing hardy hybrids, capable of resisting severe late spring frosts, which will kill or hopelessly damage flower-spikes and foliage of E. robustus and E. himalaicus, have been raised in my nursery by crossing E. himalaicus with early flowered forms of E. robustus, the result giving a fair percentage of immensely strong-growing plants, throwing spikes seven to eight feet in height, with flowers of a pale rose colour. These hybrids flower a little later than E. himalaicus and before E. robustus is out. Though not so showy as a finely developed specimen of E. robustus, the hybrid, which I named E. him-rob, has the particular advantage of being capable of safely escaping the often deadly injurious effects of late spring frosts. A very interesting and delicately beautiful plant is E. Tubergeni, which was produced by crossing E. himalaicus with pollen from an early flowered form of E. Bungei. In this plant the foliage has the deep green colour of that of E. Bungei, but is almost as broad as that of E. himalaicus, while the spikes and individual flowers most resemble those of E. himalaicus, the colour being a delicate pale primrose-yellow.

Seedlings of this hybrid either produce true E. Tubergeni or E. himalaicus, but I have not observed any E. Bungei to reappear among them. Hybrids between E. Bungei and E. robustus or E. Olgae (the latter were also raised in Sir Michael Foster's garden at Shelford) give plants in which a coppery salmon-yellow of the flowers predominates. In habit of growth and colour of the flowers some of the seedlings cannot be distinguished from E. Warei, which I have always regarded as a natural hybrid between E. Bungei and some rosy-coloured variety, but not a true species.

FREESIA.— Up to very lately these charming plants only occurred in white and creamy-yellow shades, and though yearly raised by the million from seed in France and Italy, seem to have sported very little. Crosses between the small-flowered orange-yellow F. aurea and F. refracta gave interesting hybrids, but not an improvement on either parent. The advent of the rosy-crimson-flowered F. Armstrongi from South Africa has been a most welcome addition, as this at once opened a wide field for producing some more variation of colour among these so deservedly popular flowers. F. Armstrongi itself being a rather delicate grower, I made no attempt to fertilise it with pollen of F. refracta alba or F. Leichtlini, but placed pollen of F. Armstrongi on as many different shades and forms of F. refracta, F. refracta alba, and F. Leichtlini as I could procure. The results so far have been most encouraging, and I have now a strain of tall-growing Freesias with as many as nine individual flowers on every spikelet, of which every bulb produces several, in colours varying from the palest rose to carmine and purple-red. A small percentage also came in shades of orange, buff, and coppery-rose. A selection of these seedlings, with flowers of a violet-rose shade, I exhibited in the spring of this year (1906) at one of the fortnightly meetings in the Hall, when an Award of Merit was given to it by the Floral Committee. I also attempted to cross F. Armstrongi with F. aurea and vice versa, but both ways with very poor results.

GLADIOLUS.— There are so many magnificent strains of hybrid Gladioli now being grown that I made no attempts to further improve the various races known as gandavensis, Lemoinei, nanceianus, Childsi, and others, but turned my attention to the original species. If the charming and so deservedly popular G. Colvillei and its chaste variety 'The Bride' should have been raised from G. cardinalis and G. tristis concolor (personally I very much doubt the correctness of this statement), then why should not the intercrossing of other South African species also be likely to give good results? Thus far I must own that, although a good many very pretty hybrids have been raised in my nursery, I have up to the present time only one or two strains of these Gladioli that may prove commercially useful. A selection of crosses between G. alatus and G. cuspidatus are dwarf-growing, very free-flowering Gladioli which flower in the open ground quite three weeks before the earliest of the nanus or ramosus sections, which, as is well known, precede the gandavensis and other strains in time of flowering from three to four weeks. These alatus x cuspidatus Gladioli, apart from their usefulness in flowering so early in the open ground (end of May), are very welcome additions to the Gladiolus family, as each bulb produces from two to five spikes of about a foot in height, with flowers of fair size and of a charming colour of rosy-salmon with golden-brown markings. They are admirable for filling small glasses for table decoration, and other choice floral work. This strain I named 'Express,' and from various sides I have already received letters expressing gratifying satisfaction with the habit, time of flowering, and general usefulness of these Gladioli. Other strains, results of crosses between the best and showiest of other South African Gladioli, are in course of development, and one or two, at least, seem likely to yield satisfactory results.

HYMENOCALLIS.— With a view of ascertaining the correctness of the supposed parentage of H. macrostephana, after some years' trial I managed to have the two supposed parents Hymenocallis speciosa and Hymenocallis (Ismene) calathina in flower at the same time. The results showed absolutely different plants from H. macrostephana, being much broader and thinner in the leaf; the formation and size of the inflorescence and of the individual flowers also being quite different. When in good condition, this hybrid Hymenocallis, the first authentically on record between the evergreen section Hymenocallis and the deciduous Ismenes, is a magnificent plant, with an umbel of over a foot and a half across, with large, snowy-white individual flowers, exceeding in size even the large-flowered H. macrostephana. This hybrid has been distributed under the name of H. Daphne. Crosses between the white H. calathina and the yellow, green-banded H. Amancaes gave charming mules of a delicate sulphur-yellow. These, however, have also at various times been raised in England.

Fig. 119.—Type of flower of the new hybrid Xiphion Iris.
Fig. 120.—Type of flower of Regelio-Cyclus iris.
Fig. 121.—Iris Regelio-Cyclus.
Fig. 122.—Regelio-Cyclus Iris var. Hecate.
Showing hardy character and free-flowering qualities.

IRIS.— The deep sandy soil and the climate of Haarlem seem to suit a very large portion of the Iris tribe, and from time immemorial Irises have been grown and improved by Dutch cultivators. I. Xiphium (Spanish) and I. xiphioides (anglica) strains, if raised from seed, will still yield agreeable surprises, but it is doubtful whether these really differ from those that were in cultivation a hundred and more years ago. So many species of the subgenus Xiphion being now in cultivation that were unknown to our ancestors, some eight to ten years ago I commenced intercrossing the Spanish, Portuguese, and Moroccan species of Xiphion, not using, however, the ancestors of the strain that are now known as the Spanish Irises. From these crosses various modifications at last resulted in a highly important race of very large-flowered Xiphions, of the form and shape of the Spanish Irises, but flowering quite a fortnight earlier. The flowers of this strain (which is not yet in commerce) show the same range of colours as is met with in the ordinary Spanish Irises, but the flowers are of unusual size and great substance, the falls being from 1 1/2 to 2 inches across, and the entire flower measuring over 4 1/2 inches from tip to tip. It is interesting to note that, whereas in the ordinary Spanish Irises the yellow colour is so abundantly represented, it was only in the later and latest generations of seedlings of my new strain that good and pure yellows have been developing. It is also interesting that, by continually selecting only the earliest-flowered varieties, the strain now obtained flowers nearly three weeks before the ordinary Spanish Irises, which, considering the fact that so many tens of thousands of these Irises are annually used for forcing, is another salient factor in the eventual commercial importance of this new strain.

Among species of the reticulata group the mingling of the richly coloured I. Bakeriana with selected forms of I. histrioides and I. reticulata gave charming combinations of colour among these very early-flowering gems. At present the influence of I. Danfordiae is not apparent.

The Juno group of Bulbous Irises, which in the last twelve years has received important additions by the introduction of so many Asia Minor and Central Asiatic species, presented another field of work. These Irises, usually flowering at the time when sharp, late, night frosts occur, are not easy to cross, or rather to obtain good seed from, and I find that it is only once in every four to six years that my patient labours among these give any satisfactory results, in so far as the obtaining of any seed is concerned. My earliest successes in this group came from crossing I. persica purpurea with the old I. persica, and from hybrids between I. sindjarensis and I. persica. The former I introduced under the name of I. purpureo-persica and the latter as I. sind-pers, both obtaining awards from the Royal Horticultural and other Societies. Later crosses produced the lovely I. sind-pur (I. sindjarensis x I. persica purpurea), I. pur-sind (the reverse cross), and others. The principal charms of these early-flowering bulbous Irises are their extreme hardiness, their free-flowering character, and their rich colouring.

RHIZOMATOUS IRISES.— No section offers greater interest to the plant-lover than the extremely interesting and beautiful group of Oncocyclus and their near allies the Regelia. Considering the great care that in our climate the successful cultivation of the Oncocyclus group demands, it has been my aim, by intercrossing the latter section with the easily grown Regelia, to raise a strain that would combine the beautiful and large flowers of the true Oncocycius with the hardy character and free-flowering qualities of the Regelia. I tried crosses both ways, but soon found that hybrids raised from the Oncocyclus with the Regelia did not possess any more vigour than their seed-parents, whereas the Regelia section (I. Korolkowi, I. Leichtlini, I. vaga, &c.) crossed with pollen of the Oncocyclus gave birth to a hardy, free-growing and free-flowering race (fig. 120). Some of the varieties from these crosses have now been in cultivation in my nursery for over eight years, and the accompanying illustration, which shows a portion of my stock of Iris Hecate (one of the varieties raised from I. Korolkowi violacea x I. iberica insignis), speaks for itself, that in point of vigour and free-blooming qualities this new race, which has been distributed under the name of Iris Regelio-cyclus, leaves nothing to be desired. Another point in favour of this race is that in the open ground it flowers with the very earliest members of the Rhizomatous Irises, such as I. praecox, and some pumila varieties, preceding the host of ordinary bearded Irises (germanica) by from three to four weeks. From the Regelia parents they also inherited the desirable gift of producing two flowers in each scape, a second flower taking the place of the first on withering. Especially beautiful in this strain are the hybrids of selected varieties of I. Korolkowi type x with I. susiana and I. iberica, and also crosses between I. Korolkowi violacea with the purple-red I. Mariae. Strange to say that a cross between I. Korolkowi concolor (which I find is not quite so vigorous as are the other Korolkowi varieties) and Iris Mariae — reputed to be one of the most difficult of the Oncocyclus tribe — produced a group of exceedingly vigorous varieties, of which the now well-known 'Artemis,' a very vigorous variety with rich purple and violet-black coloured flowers, may stand as the type. Without going into cultural details, the fact that the stock of some of the varieties (all of course propagated by division from single, selected specimens of special merit) in many cases now consists of several hundred plants, conclusively shows that this race has come to stay in our gardens, and will not ultimately dwindle away as the pure Oncocyclus always do.

Naturally my attention also turned to the hybridising of the best varieties of the ordinary bearded Irises (germanica) with the Oncocyclus. A beautiful and very large flower came out of a cross between I. iberica and I. germanica macrantha [Iris Ib-mac], the flower measuring not less than six inches across and of a beautiful blue, with broad, spreading falls, heavily bearded, and with a dark, black-blue central spot. Unfortunately in our climate, with its damp summers, we cannot give to these plants the dry, baking heat of southern countries, and the plants consequently are very shy-flowering, as are also similar crosses of Oncocyclus with I. pallida and I. germanica. Hybrids raised by Sir M. Foster, however, among these groups, notably I. paradoxa and I. iberica crossed with I. variegata and I. sambucina, are almost as free-flowering as is the ordinary I. germanica.
[Visit Sharon McAllister's Cyberspace Iris Garden for more iris of similar breeding, Iris lortetii, Iris iberica ochracea, Iris 'Aphrodite', Iris 'Polymnie', and Van Tubergen's hybrids listed in Les Iris Cultivés 1923]

NERINE.— Notable hybrids in this beautiful group of autumn-flowering bulbous plants arose from the intercrossing of Nerine pulchella [flexuosa] , of which I grow an almost evergreen variety, with the best of other species and hybrids. I cannot understand why all the plants which were raised from this cross, both ways, developed a much later blooming character than either parent, so much so, that they usually are about at their best the second and third week in December. These hybrids are very vigorous, with foliage 1 to 2 feet in length, and with flower-spikes of corresponding height. The range of colours in these hybrids is from pale rose to bright carmine, and the umbels, composed of very numerous flowers, measure from six to seven inches in diameter. Unfortunately these hybrids seem to be absolutely sterile, so that I fear it will be very difficult, if not impossible, to further develop this strain, which, even as it is now, proves very valuable for producing bright-coloured effects in the cool conservatory at the dullest time of the year.

NARCISSUS.— Crosses among these have for the last eight to ten years been largely made in my nursery, and some good varieties have been raised. My observations on this class of bulbous plants, however, do not materially differ from those of other modern raisers of the Daffodil, and do not therefore call for any particular comment.