IRISES OF THE FUTURE. W.R.Dykes

THE GARDENERS' CHRONICLE.
May 28th, 1921.

IRISES OF THE FUTURE.

W. R. Dykes

IT is never easy to prophesy correctly, even if successful prophecy is little more than intelligent anticipation. The following notes, therefore, are intended less as an indication of the future than as possible suggestions.

Among the early bulbous Irises there seems little hope of new developments, unless we can hold in check the fungous disease which plays such havoc among the bulbs. If we could overcome and eradicate this, there would be no end to the delightful series of beautiful hybrids which might be raised by crossing the richly coloured, velvety-petalled I. Bakeriana with the other species. The yellow I. Danfordiae might also be used to give us entirely new forms.

The Juno species seem to suffer from an undeserved neglect, for there are few finer garden sights in April than a large mass of the glistening, sturdy foliage of I. bucharica, closely set with the large white and yellow flowers; while the endless variety of colouring to be found among seedlings of the gorgeous I. Rosenbachiana well repays the patience which is needed during the three or four years that the bulbs require to grow from seed to flowering size. The later bulbous Irises, comprising I. Xiphium, the Spanish Iris and the kindred species, seem to have fallen under a cloud, from which they will hardly emerge until some remedy is found for eel-worm in the soil, for this pest appears to be as fatal to Spanish Irises as it is to the Narcissus. If this can be overcome, the multiplication of the florists' varieties, both of the Spanish and of the Dutch Iris, will go on; but we cannot expect much from their combination with any of the allied wild species, though these are distinct enough in themselves. They do not seem to combine well either with one another or with I. Xiphium. Thus I. filitolia, when hybridised, loses its magnificent red- purple colour ; I. Boissieri has the long hairs of its beard shorn down to half their length; while the clear golden yellow of I. juncea becomes dull and streaky.

Of Oncoyclus and Regelia Irises I am distinctly more hopeful than there seemed any justification for being a few years ago. Experience seems to show that these must all be dug up annually about the middle of July. The rhizomes may then be left lying out on the ground for a few days, provided that the sun is not too incessantly brilliant and scorching. They should then be trimmed of their leaves and be stored away, preferably in perfectly dry sand, in a well-ventilated, dry place, until the first week in October. The rhizomes and the roots should, with this treatment, remain firm and be ready to start into root growth as soon as they are replanted in rich, well- drained soil. At one time it used to be thought that the soil must first be beaten and trodden down until it was almost as hard as a rock, but this seems unnecessary, in view of the way in which these Irises flourish in the loose sand of Haarlem and in the drier, but equally light, Surrey sands.

To my mind, the fault of the Regelia-cyclus hybrids that are already in commerce is that they are nearly all of them mere colour variations of the same type of flower. When we remember, however, how utterly different I.paradoxa is from I. susiana and from I. iberica, and how each of these latter differ from the aptly named I. acutiloba and from the rounded, self-coloured flowers of the purple I. Mariae and its yellow counterpart, I. urmiensis, I cannot help feeling that crosses with these species might give us new types. Evidence to confirm this exists in the pleasing results that have resulted from crossing I. acutiloba and I. Sari with I. Korolkowi. The former gives very floriferous hybrids with the extended falls of acutiloba and the prominent veining of Korolkowi, while the latter retains the shape of I. Sari and something of the colouring that won for that species the name of the Wolf Iris, I. lupina.
No hybrids have yet appeared of I. Hoogiana, the last discovered and most astonishing member of the Regelia section. Its unveined, self-coloured flowers of pale or dark blue- purple are so beautiful that it seems almost sacrilege to attempt to hybridise into them the veinings and dottings of the other Regelia and Oncocyclus species, with which there would probably be no difficulty in making crosses.
Nothing has, so far, been said about the great class of Pogoniris or bearded Irises, which to so many comprises practically all the Irises that they know. Here the tendency is to aim at increased stature and a more widely branching habit in the inflorescence, qualities which are obtained by using as parents I. trojana and other giant species, such as I. mesopotamica and I. cypriana, which have now become more widely distributed. Whether we should aim at self-colours or at variegation in the flowers is a matter of personal taste and it is devoutly to be hoped that no self- constituted body of florists will attempt to lay down strict canons on this or on similar points and then try to ensure that all our Irises should conform to these canons.
For garden ornament it is hard to find anything more decorative than self-coloured pallidas, which can be obtained in a long series of shades from a deep blue-purple to a pale pink. If pallidas are, as a whole, later than the so-called I. germanica, it is easy to obtain an early race by crossing I. pallida with I. Albertii, from Turkestan. The characteristic veining on the falls, which ends so abruptly and which is typical of the species, is not sufficiently prominent, except at close quarters, to spoil the effect of self-coloured flowers. At the other end of the season something might be done towards prolonging it by using the late-flowering Black Prince. Seedlings of this tend to retain the late-flowering habit, and, as there is a large dose of I. variegata blood in Black Prince, forms with yellow standards are sure to appear among them. It remains for the hybridiser to get rid of the stunted stem, the crowded inflorescence, and the ugly form of the flowers, with their erect, widely separated standards.

Among the Evansias something good might come from the crossing of I. Wattii, which does so well when planted out in a cool house. It ought to cross with I. japonica and possibly also with I. tectorum and I. Milesii, if these two could be forced into flower early enough. I. tectorum and I. Milesii seem themselves to be so closely related that it is surprising that all attempts to cross-fertilise them have hitherto ended in failure, though a combination of the large flowers of I. tectorum with the tall stem and sturdy foliage of I. Milesii ought to make a most effective garden plant.

Among the Apogons or beardless species there is still scope for much work in hybridisation. The members of the various groups of obviously closely related species hybridise fairly readily with one another, and it is also possible to cross members of different groups with one another. For instance, the Californian I. tenax will cross with the Chinese I. Wilsonii, and the hybrid bears curiously speckled, dull purplish flowers with a yellow ground. I. Douglasiana crossed with the Himalayan I. Clarkei gives a mottled, pinkish flower of no great merit, but, when crossed with the Chinese I. chrysographes, gives a beautiful flower of a crushed strawberry colour, with gold veining on the falls.
Those who will take the trouble to raise seedlings should turn their attention to the group of Californian species, of which it seems true in many cases that no two individual plants produce flowers of the same shade of colour. The variety to be found among seedlings of I. Douglasiana, I. tenax, and I. macrosiphon is endless, and, as the plants flower in two years from seed, no one need hesitate to embark upon their cultivation. The seeds should be sown in pots or pans, and the young plants are best grown on quickly under glass, so that they are large enough to be planted out in the open in their permanent positions in May if possible, or, at any rate, before midsummer. They should then grow rapidly and develop before the autumn into plants of sufficient strength to pass safely through the winter.

The Sibirica group has lately been extended by the new introductions from China, and all its members seem to hybridise readily with one another. Much may be done with the older and well-known species, I. sibirica and I. orientalis, for the large flowers and brilliant colouring of the latter can be readily combined with the tall stature and floriferous habit of the former, while 'the crossing of the white with the blue forms of either species will give seedlings a nearer approach to a true sky-blue than is found in any other Iris. The yellow Chinese I. Wilsonii will give a yellow ground to I. sibirica and to I. Delavayi, and the combination is particularly pleasing in the latter case.

Two of our native species, I. Pseudacorus and I. foetidissima, do not seem to lend themselves at all readily to hybridisation with others. I. Pseudacorus seems to reproduce itself with whatever pollen the flowers are fertilised, and nothing ,seems able to fertilise I. foetidissima except its own pollen. It is true that there exists a plant which appears to be a hybrid between I. Pseudacorus and its closest ally, namely, the American I. versicolor, but no record exists of the origin of the hybrid. Its sterility is some indication of its hybrid origin and its intermediate position between the two above-named species suggests that they were its parents.

Hybridisation is a fascinating pursuit, and enough has already perhaps been said to show that much remains still to be done among Irises, especially when we remember that crosses that have often been tried in vain may at length prove successful.

W. R. Dykes.

The above article has also been published in the book 'Dykes on Irises' compiled and edited by George Dillistone, a reprint of the contributions of the late W. R. Dykes to various journals and periodicals during the last twenty years of his life.

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