Les Iris Cultivés 1923 p. 74-81
Société National d'Horticulture de France Commision des Iris

A. J. BLISS (F. R. H. S.)

There are three methods of plant breeding, and by each good results may be, have been obtained. By saving and sowing the seed from some exceptional flower and, in the case of annuals, with careful and continuous selection for some years, races of new and beautiful flowers have been produced. A somewhat more definite method consist in collecting together the finest varieties procurable, including, where possible, new species, and either hand fertilizing at random, or allowing them to be cross fertilized by insects. Among the great number of seedlings that can be thus obtained, there is always the possibility of some few occuring which by a rare combination of characters will prove to be of exceptional merit, or even quite new departures. This may be called the extensive method. Then there is the third method, — the intensive method, — of selecting the parents and making each cross-fertilization with a definite aim. And this in the long run, if records are kept, is productive of the widest and most far reaching results, for each step forward that is made can be used intelligently for still further improvements, an increasing knowledge of the material worked with, is gained; and possibilities are not only suggested, but the way of obtaining them is indicated.

When, therefore, one proposes to take up the cross-breeding of any flower with the object of improving it for the garden, it is well to have some definite aims. Not that these aims which one start with will necessarily be our final or only aims. Far from it. For as the work progresses the horizon ever widens and possibilities appear which at first we could hardly have thought of, and aims that in our ignorance seemed possible have, with the experience gained, to be abandoned as unattainable, or, at least, modified and limited. It is, indeed, one of the charms of plant breeding, that you launch out into the unknown, along a road the end of which you cannot [75] foresee, but with the assurance that, with perseverance, you will find there more than you sought.

The particular aims, in which I was chiefly interested, were to obtain a crimson Iris and a plicata with a golden yellow ground. I had the desire to break new ground and such varieties were entirely unrepresented in bearded Iris at that time. All other aims which I had in mind were more of the nature of improving varieties that already existed. Of the more general aims, which every conscientious breeder must attend to in seeking to improve flowers, special consideration was given to increasing the substance and broadening the segments.

Neither of the two special aims, — the crimson Iris and the yellow ground plicata, — has yet been attained, but much may often be learnt from failure. The work done will perhaps not be entirely wasted, and may help to pave the way, if the experience gained is shared with these who may take up the quest, and some account of my attempts may be of interest and save others from much barren labour. The advances made towards a crimson Iris are very slight and seem to show that, if it is possible, the right direction to work has not yet been found. It may be that it is unattainable, though I do not think so. But there is one consideration why it may be, at any rate, specially difficult. Willstatter (quoted in The Anthocyanin Pigments of Flowers, by Miss M. Wheldale) expresses the opinion that "variation in flower-colour largely depends on the presence of other substances, acids, alkalies, salts. etc., in the cell-sap". The blue type of Centaurea, for instance, contains the alkaline (potassium) salt of the pigment of the purple variety, To put it more fully: — "In Centaurea flowers, there are three modifications of one anthocyanin pigment: a purple pigment, cyanin, which is itself free acid; a blue pigment, which is the potassium salt of the purple...; and a red pigment, which is the oxonium salt of the purple with some organic acid".

The pigment forming processes are not the same in all flowers and it does not follow that they are the same in Iris as in Centaurea, but it is significant that red is associated with acid, and blue with alkaline substances. As is well known, bearded Iris grow best in a calcareous soil, and become unhealthy if the soil is at all deficient in lime. That is, they thrive in comparatively alkaline medium and resent an acid condition. It does not follow that they would therefore be unable to elaborate the necessary acid substances for the production of a red pigment, for there are many plants which thrive in a calcareous soil which have red flowers, but it might well be that it would be less easy and less natural to develop the acid than the alkaline type of pigments. [76]

I do not think that a crimson Iris is unattainable on this consideration only, but it suggests that it might be best to choose those varieties which are least affected by lack of lime in the soil, if otherwise suitable. Such varieties may be recognized by their comparative freedom from the spot disease (Heterosporium gracile) in soil deficient in lime.

Many of the crosses made in the course of my experiments are not worth recording, as they were made rather with the object of exploring every possible combination than with any expectation of obtaining results in the desired direction. But three definite lines were pursued and carried through long enough to warrant drawing some conclusions.

1° Intercrossing pallida only, choosing the reddest of the red-purples which were available. 2° Crossing variegata forms (including self yellow and squalens) with "red" pallida and neglecta to test whether there was any hope of obtaining a crimson through the combination of the violet-purple of pallida with the yellow of variegata. And under this head may be included experiments with flavescens. 3° Crossing plicata with all other types.

1° The intercrossing of pallida, where they were undoubtedly pure pallida, gave no advance whatever towards a red. But including in these experimental crosses all varieties which were formerly classed as pallida such Assuerus, Queen of May and rubella which are obviously not pure pallida, as well as such varieties as Leonidas, in which the alien mixture is not so evident, many "red" seedlings were obtained, which though no nearer a crimson than Assuerus (the reddest variety then available) were improvements in other respects in height, habit, size and form of flowers and brightness and depth of colour. These were used in subsequent experiments in crossing with variegata and plicata forms. Only one seedling, Roseway, was actually redder, that is, freer from the purple tone and that only slightly though distinctly. Otherwise, none were really any improvement on Verdier's Edouard Michel on the whole, though generally brighter coloured and freer flowering. They were however useful for further experimental crossing, especially as Edouard Michel is a poor seeder, since, having tested the varieties originally used, I now knew which contained flavescens or variegata or plicata in their ancestry, and could observe the different effects of these varieties or species in future combinations.

2° With the idea that possibly a crimson could be obtained by some proportion of the combination of the yellow of variegata with the violet of pallida, crosses were made of the above mixed pallida with red squalens and red neglecta (using chiefly Jacquesiana and Cordelia), and also with the self yellow Mrs Neubronner. To sum [77] up the results, the direct combination of pallida violet and variegata yellow in, any proportions, had no tendency to produce red, and my conclusion is that the mixture of these two pigments alone could never give a crimson.

As there are other yellow pigments, — soluble or sap yellow pigments, — besides the more common plastid yellow, on the possibility that the yellow of flavescens was different from the yellow of variegata, crosses were made to test the effect of flavescens yellow in combination with other types. I had all the more expectation of finding it a reddening factor since from one of the earliest crosses made of Queen of May x Thorbeck a seedling appeared indistinguishable from flavescens, which seemed evidence that flavescens was in the parentage of Queen of May. The results have however been very conflicting. Some crosses with flavescens, when either a plicata or a squalens or an amoena, or all three were also in the ancestry gave red or rose toned seedlings. Crosses with a variegata, flavescens x Maori-King gave some seedlings with a brighter colour in the falls than ordinary variegata varieties, viz. Glitter, but from the same seed pod came also blue-toned amoena, and lastly, from and cross flavescens x macrantha came one of the bluest-seedlings I have raised viz. Blue bird. It seemed, therefore, that the reddening effect was due to the presence of one of the other types in the parentage, and from other results, most probably plicata. But so far as my experiments have gone, it seems improbable that plicata is in the ancestry of Queen of May, for only one plicata has appeared out of 33 seedlings from crosses of Queen of May by a plicata, and that it is most likely, an accidental self seedling.

3° One of the earliest results observed from crosses of plicata with almost all other types was the number of cases in which red toned seedlings appeared. The explanation that first occurred to me, — that the plicata type might be due to two complementary factors, one of which by itself — had a reddening effect, seems no longer tenable in view of later results, and I have no alternative theory to suggest except that possibly some other species such as balkana in the ancestry of plicata. This is, however, a mere guess, based chiefly on the distinction heard of plicata. This effect of plicata (in certain combinations, for there are notable exceptions) is, however, I am sure, a fact, and a mere impression not as it is the recorded result of very many diverse crosses. Among the old standard varieties, also plicata, is in the parentage of Assuerus — the reddest red — pallida and in that of Jacquesiana, the reddest of the red squalens. And it can hardly be a coincidence that all my reddest toned seedlings have plicata in some degree in their ancestry and all that have been tested have proved to be heterozygous for [78] the plicata factor. Roseway = (Assuerus x Queen of May) is heterozygous for plicata, while Dora Longdon (= Queen of May x Cordelia), which has no plicata in it, shows much less red and more yellow. Red star (G. 141 (10), the pedigree of which has been given in the Gardener's Chronicle, Feb. 14. 1920) though not a large flower, is a real advance in colour. It is a seedling from a series of crosses in which I combined Mme Chereau, Cordelia, Queen of May and Assuerus. From the same pod of seed there came two plicata out of 15 red pallida-neglecta. Susan Bliss, a very pure rose-pink, and Saranac, the reddest pallida form I have obtained, are sister seedlings with a long pedigree.

Several plicata appeared from the same seed pod. The pedigree of Evadne and Auburn is:

Lastly, citronella, which is remarkable for the bright and clear crimson veining of the falls, has plicata in its ancestry, both from Mme Chereau x Jacquesiana.

Perhaps after all, the crimson iris, when it comes, as I am sure it will someday, will come unexpectedly as the result of a rare breaking of some linkage of factors that at present defies direct effort, and it will be a mutation.

The yellow-ground plicata, is also not yet obtained, but it is a much near attainment than the crimson Iris. In 1907, I first flowered a plicata with a pale sulphur ground, and perhaps Mercedes is even older. Since then, many of the same type, — squalens-plicata, — have been raised, and they show that the plicata type factor does not affect the yellow ground colour, the weakening or dilution of it in these squalens-plicata being most probably due to other and [79] quite distinct factors, as shown in analogous crosses, where plicata is not present. Now, citronella and Miss Sturtevant's Shekinah, in which a full primrose yellow has been obtained in the pallida type, make it almost certain that the full yellow ground can also be obtained in the plicata type.

Though these two particular aims have not yet been attained, improvements in many other directions have come, and in the, general aims of increasing the substance and broadening the segments, the results have been beyond all expectations. In Dominion, these most desirable qualities seem almost to have attained the limit of possibility. Dominion came from a single seed from a variety which I had as Cordelia crossed by macrantha. I am not sure if it was the true Cordelia, for I lost the plant and the plant of Cordelia I now have does not seem quite like my recollection of the original one, through certainly of the same type. I have made the same cross several times since and the few resulting seedlings show many similarities with Dominion, — in the strong blue-green foliage, and even, in a far off way, in the flowers, but none approach Dominion's remarkable size and substance and breadth of falls. So I am inclined to think that Dominion is in some way a mutation, — possibly a tetraploid like De Vries, Oenothera gigas, which is calculated to appear only once out of 900,000 seedlings! However, it transmits its qualities to its progeny, and Bruno is larger, of equal substance, and has even broader falls, which are of the richest velvety red-brown.

It is worthy of note that exceptional flowers, showing a great advance on their parents, have nearly always come from crosses that produced very few seed, generally only one or two.

These may be considered to be difficult crosses and, in my opinion, they demonstrate the value of making «out-crosses», that is, crosses of widely dissimilar parents. I imagine that the comparative incompatibility of the germ plasms induces breakages of the factor linkage which, in the case of more normal unions, would always hold together. Such crosses require much patience and perseverance, but the rewards are commensurate with the labour. As an example, Pioneer came from one of two seed from a cross in which Paladin was the pollen parent (it has so far proved entirely infertile as a seed parent). It is the only seedling I have yet obtained from Paladin though more than 200 crossings have been made. Often such exceptional seedlings are sterile or nearly so, but Pioneer is a fairly free seeder and so at last it will be possible to carry on a strain that has exceptionally fine qualities and which has germanica in its ancestry; Paladin being a seedling of germanica x macrantha.

Dominion came from one seed; Bruno from 2 seeds; Gabriel [80] 2 seeds; Patrician, one seed; Blue bird, one seed, Phyllis Bliss from one seed. The only real exception is Samite (= flavescens x Mrs Neubronner) of which there were 22 seed. This, though not an exceptional flower, from a garden point of view, is as remarkable, in proportion, as Dominion for the great advance on its parents, in substance and breadth of falls. Clematis (= Cordelia x Princess Beatrice), which is a sudden departure in form, was from six seed.

Cretonne (= Assuerus x Maori King), which is certainly remarkable for the amount of colour that pervades the whole plant, came from 10 seed; none of the other seedlings showed special colouration.

Citronella, which is really only exceptional in that it is a new combination of colours already in the parents, came from 16 seed. Titan; Cardinal and others of the Dominion race though remarkable flowers, are not an advance of the same kind, — their exceptional qualities being simply derived from their parent Dominion.

In illustration of the diversity of type which may appear from the same cross, Da Guesclin, — a rich violet-blue neglecta of Monsignor type, — and Sweet lavender came from the same pod of seed from a cross of Mme Chereau x Cordelia. The Sweet lavender type is the rarer one appearing once to about 12 or 16 of the Monsignor type.

To any one unacquainted with the breeding of mixed hybrids, it would also seem surprising that Azure, — a deep violet blue neglecta, — and Dusky Maid, — a purplish brown squalens, came from the same pod of seed of the cross Leonidas x Maori King.

Knysna (= Maori King x Jacquesiana) illustrates how, probably, the plicata factor (in Jacquesiana) keeps the yellow of the standards clear, similar crosses of a variegata by a squalens, when no plicata is present, generally result in standards of a brassy yellow.

Francina (= Assuerus x Mme Chereau) illustrates the possibility of modifying or transfering colour characters by crossing with a variety of the desired colour, and then crossing back again. Assuerus is heterozygous for plicata, and by crossing it with a plicata (Mme Chereau) one half of the seedlings will be plicata, and in some of them the red colour of Assuerus will come over together with the plicata type. squalens-plicata may be produced in a similar way.

Light or yellow margins in the falls of variegata are common enough, but a really defined margin appears to be very difficult to obtain. Marsh Marigold (= Maori King x an amoena seedling) was the only variegata seedling with a really defined yellow margin out of several hundred from various crosses.

My experience with white Iris has not been very large until quite recently. Mrs H. Darwin, on which I relied at first besides being a recessive white; gave flowers of such bad form that all have been destroyed. [81] albicans and germanica alba appear to be dominant whites, — giving white flowers in the first generation, — and promise good and even exceptional results. But their earliness makes it difficult to cross them with most of the June flowering bearded Iris, and they are poor seeders, with infertile pollen. My only interesting white from albicans, at present, is Berenice (= albicans x trojana superba). It is a pure white, with golden yellow reticulations on the hafts (in place of the brown of trojana) which seems to show that in these reticulations there is yet a third kind of yellow pigment besides the variegata and flavescens yellows. Amoena give whites (generally tinted pink or porcelaine) from crosses with some squalens, e.g. Judith x Thorbeck; Thorbeck x Jacquesiana; Queen of May x Thorbeck. These amoena derived whites are however unsatisfactory and since the whites derived from plicata, which are now appearing, have much finer flowers and are freer flowering, all the amoena whites have been discarded. I do not yet fully understand the genetics of the plicata derived whites flavescens x aurea or Mrs Neubronner give cream whites, often exceedingly free flowering, but with small flowers.

From the collected results of many experimental crossings it has been possible to draw general conclusions, which are also of practical use to breeders, regarding the origin and constitution of the types, (once regarded as species), — neglecta, squalens and amoena. I have given the reasons for these conclusions in the Gardener's Chronicle. Feb. 14, 1920 and in The Journal of the Royal Horticultural Society, Vol XLV, parts 2 and 3. Amoena varieties are simply colour varieties of variegata, white taking the place of the yellow, and purple or violet-blue taking the place of the red-brown of the falls of variegata. The relationship between neglecta and squalens is of the same nature; neglecta being, practically, squalens in which there is no yellow. Both neglecta and squalens come, — in about equal numbers, — from crosses of pallida x variegata varieties.

Furthermore, from a long series of crosses it has been demonstrated that the plicata type is recessive to all other types, except perhaps some whites.

Some Bliss introductions