Jour. Roy. Hort. Soc.
vol. 25 (1900)
Hybrid Conference Report pp. 280-287
A FEW NOTES ON REPRODUCTION IN HARDY PLANTS BY MEANS OF HYBRIDISING SPECIES AND CROSSING VARIETIES.
By CHARLES STUART, M.D.,
Fellow Bot. Soc. Edin., Member and formerly President of the Berwickshire Naturalists' Club, and Member of the Scottish Alpine Botanical Club.
WHEN I had the honour of receiving the kind invitation of the President of the Council of the Royal Horticultural Society to attend the Conference of Hybridists at Chiswick, and contribute a short communication, I felt somewhat diffident as to the nature of the information I would be expected to give. Upon consideration I came to the conclusion that, as the scientific element would be better elucidated by the many distinguished botanists whose names appear on the list than I ever could hope to do, it would be more interesting to give a short statement of an amateur's attempt to raise new varieties of hardy plants than to enter into a detail of the process of hybridity. Like many others, I have had in my attempts many disappointments, perplexities, and failures in the results of these operations, but upon the whole there has been much pleasure, and some profits. As a rule very careful selection is required, as even with all the skill of the hybridist many of his seedlings are deficient in some vital point of constitution, however sound the parent may be in that respect. A small minority is all that need be expected to be better than the parent in crossing varieties, and besides an accurate knowledge of quality is necessary to ensure "the survival of the fittest." No more delightful satisfaction can be experienced by the amateur florist than to watch the development of the beauties of his seedlings from which he expects an advancement in quality. It is not in every season that the elements are propitious for hybridising operations; and even when successful crosses have been effected, do the results always satisfy the anticipations of the operator? The month of June, 1899, has been an ideal one to the seedling raiser. There has been more continuous sunshine than for many years. The temperature at the same time has been very high, and the weather on the whole has been very suitable for crossing hardy plants as well as exotics. The early spring was the worst on record, and in consequence the Primulaceae, from which so much was expected, are a miserable failure as regards seed. With this preface I shall now endeavour to give a short statement of work carried out during many years of my life.
MIMULUS TIGRIOIDES.—More than forty years ago the late Mr. Robert Stark, a well-known Edinburgh botanist and florist, brought me & plant of Mimulus cupreus, a native of Mexico, saying, "There is the very thing for you. Cross the garden Mimulus with the pollen from this plant, and you will get something different from the ordinary forms." At the time I had no plant of Mimulus in the garden, but I speedily got 'Scarborough Defiance,' a good Mimulus in its day, and potted it and M. cupreus, growing them together in a cool greenhouse. In the month of May, when they were both in bloom, I removed the stamina in an imperfect condition from several flowers of 'Scarborough Defiance,' cutting off the remaining flowers on the plant, after examining the stigmas with the glass to see that there was no pollen already there. Waiting till I saw that the stigmas had matured, I took the pollen from M. cupreus, and dusted over the two-lipped stigmas of 'Scarborough Defiance.' They showed an irritability well worthy of observation. On depositing the pollen, the two lamellae or plates of the stigma clapped together, effectually protecting the pollen and preventing the intrusion of insects. Tying a piece of scarlet worsted round the stems and footstalks of the fertilised flowers, I waited patiently for the maturation of the seed pods, which contained a large quantity of minute seeds. The seed, as you all know, is of a dust-like character, and requires careful manipulation to get it to germinate and produce plants; Having prepared some seed pans, filled with vegetable mould and sprinkling of sand, finely sifted, watered the soil, and allowed it to drain, I sowed the seed, pressing it into the soil with a piece of glass. Placing the seed pans on a moistened surface in a shady situation, a good stock of seedlings appeared, and got past the stage of childhood.
In the following spring, upon their flowering, I found the whole to be identical in character. The plants were very dwarf in habit like the pollen bearer, short jointed, and the stems of a reddish-brown colour. The flowers were much smaller than the seed bearer, yellowish in colour, and covered with minute dots; clearly demonstrating the powerful influence of the pollen of another species, and keeping more to the character of the pollen bearer, and proving the dwarfest of the Tigrioides section of the Mimulus family. This hybrid was sent out by Mr. Cannell, of Swanley, and was a favourite in its day for bedding and for edgings to flower beds.
COLOURED ZONAL GERANIUMS.—In 1864 or earlier the floral world was curious to know how a tricolour-leaved Geranium, named 'Mrs. Pollock,' had been obtained. Mr. Grieve, a native of Berwickshire, but at the time I mention residing near Bury St. Edmunds, had the honour of originating this particular strain. His work I have verified in every particular. He found by crossing Geranium Golden Chain with Golden Pheasant that he obtained a strain which has produced the most wonderful results in coloured leaves that can be imagined. He found his plants very weak in constitution, and some would not live at all, and he was at his wits' end. To give vigour of constitution he chose a dwarf green horse-shoe Geranium as the seed bearer, taking the pollen from the high. coloured varieties. The higher in colour his seedlings were the more tender in constitution they proved. Taking a strong-constitutioned horse-shoe-leaved Geranium as the seed bearer, with an extra dark zone for my seed bearer, a fine sunny summer, not so common now as then, afforded me facilities for fertilisation of the flowers. As the flowers of the Geranium above mentioned opened the stamina were carefully removed before the maturation of their pollen. At the warmest period of the day, when the stigmas were in condition, the pollen from some of Mr. Grieve's high-coloured seedlings was dusted over the three cleft stigmas of the horse-shoe, having in the first place observed with the glass that no pollen grains had been deposited there by insects. Carefully enveloping the flowers operated on in net bags tied with scarlet worsted, the flowers fertilised speedily withered. Eventually I succeeded in harvesting a certain amount of seed. The silky, feathery awn, where it is attached to the axil, soon shows when the seed is ripe, and requires to be sharply looked to, for if not carefully protected would soon fly away.
On ripening, the seeds were gathered and sown at once in pans, placing them in gentle heat. The seedlings appeared in three weeks; a certain number showed n stripe of white, or rather cream colour, on their seed leaves. All having green seed leaves were thrown out. The produce was grown on in pans and seed boxes for some time, a large proportion showing a provoking amount of green; a smaller proportion parti-coloured leaves; a still smaller proportion white or yellow; completely etiolated individuals speedily died a natural death. After careful nursing through the winter there were a considerable number to prove in the spring: those having parti-coloured leaves I found most inclined to send out a branch with the true characteristic tricolour marking. The branch was cut off and struck; the plant so raised kept its character most wonderfully. Of the collection of seedlings some did not break or develop their true character for years, although it was easy to see the golden blood in their veins. In our moist climate of Scotland I found them very delicate, and inclined to damp off in the winter season. In dry summer weather no more beautiful objects could be looked at than a cold frame filled with tricolour and silver-leaved Geraniums, although like many other good plants they seem to have gone out of fashion, probably assisted by damp seasons, when they were difficult to keep.
TUFTED PANSIES OR VIOLAS.—The Garden Pansy has been a favourite with all lovers of flowers, and its florist varieties have been brought to a high state of perfection and beauty. Its origin is still uncertain, our native Viola tricolor, crossed with Viola altaica, having the honour of furnishing the original plants from which all the florist varieties have been derived. As far back as 1835 the march of improvement in quality of petal, size, and shape commenced; and the illustrations of the Pansy in the floricultural magazines of that period give some idea of the immense improvement that has been brought about by crossing varieties of the Garden Pansy. With its advancement in refinement, however, it was found that its constitution did not improve, and costly varieties had a habit of suddenly dying in hot weather. This led hybridists to turn their attention to endeavour to secure a hardier race by crossing some of our wild species with the Garden Pansy, the result being the plant now popularly known as Viola, but a still better name is Tufted Pansy. At present it is a plant with a very dwarf habit, abundance of flbry roots, moderately large flowers, and a compact tufty appearance. The fibry roots enable the plant to withstand the changes of temperature and climate which affect plant life, and which we are all so well acquainted with. In general, one man succeeds in crossing two plants of different species, while another takes up the idea and carries out this fertilising process a step farther. In 1873 Mr. B. Williams, of London, succeeded in getting true hybrids between Viola cornuta of the Pyrenees and the Garden Pansy. Following up his idea, I fertilised Viola cornuta with pollen from Blue King Pansy (a bedding Pansy), and ripened a pod containing twelve seeds, which were at once sowed. Every seed germinated, and in the following spring the plants flowered with flowers of identical character, the long spur or horn seen in the under petal of V. cornuta being very conspicuous. These flowers were quite distinct from anything in the Viola family I have over seen. Indeed it is safe to write that the cross had never been made till the plants of Mr. Williams and those above mentioned appeared. I tried to reciprocate the cross by taking pollen from V. cornuta and applying it to the pistil of the same family ('Blue King'). The produce was a failure, and many failures besides that recorded have occurred to other persons who have endeavoured to raise Tufted Pansies in that manner, the result being straggling habits in the plants and large Pansy-looking flowers. The next step followed with the seedlings from V. cornuta crossed with Pansy 'Blue King' when in full bloom was to fertilise the blooms with various coloured Pansies, the results being flowers showing almost every colour except yellow. The plants were of true tufted character, with blooms showing the horn or keel of V. cornuta species. Afraid lest these crosses should become too similar to the Pansy, I took pollen from the original cornuta hybrids and fertilised some blooms of those above described. "The stocks being sound this in-and-in breeding does not necessarily impair the vigour of the race." Nor did I find it so in this instance. If any flaw in their constitution existed, there is no doubt that, sooner or later, a similar defect would ultimately appear in the progeny; but this did not happen here, as the produce of the cross proved healthy in every respect. These seedlings had flowers three times larger than V. cornuta, and were of various colours, very tufty in habit, some almost proliferous, also most abundant in blooming. Mr. Barron, Garden Superintendent at Chiswick at that time, induced a number of growers of Violae to send selections from their stock to Chiswick Gardens in order to test by comparison when growing together which were the best varieties. His wish was responded to by a large number of growers, and a very interesting exhibition was the result. Mr. Barron wrote to me at the time inquiring howl had got the cross, at the same time stating that these plants had flowered more continuously than any of the varieties being tested there. Upon affording the information required, the Floral Committee of the Royal Horticultural Society awarded me six First-class Certificates for varieties 'Lady Susan Suttie,' 'Mr. Williams,' 'Hillside Beauty,' 'Ormiston Georgia,' and 'Dr. Stuart.' These certificates were awarded in 1874-5. The varieties were now grown on, by myself and friends, for several years, and were found to be excellent bedders and very hardy in withstanding climatic changes. As a bedding plant the Viola is peculiarly adapted to our Scottish climate, delighting as it does in cool, moist soil. The flowers are capable of making a continuous display in the flower-beds to compete with it, and by hand-crossing the varieties are numberless. I may mention here that these varieties were all more or less rayed in the centre of the flower. A floral friend remarked, "With regard to a white-rayed self, if you could only get that flower, without any rays in the centre, it would, in my opinion, be an improvement." Keeping a sharp look-out on the seedling beds, I did not succeed in obtaining what I was searching for till the year 1887, when, for the first time, I observed a white flower, entirely rayless, dwarf in habit, and with most pronounced almondy perfume. The plant was removed and propagated, and grown on next season, some blooms being sent to Mr. Robinson, editor of The Garden newspaper, who at once sent a favourable report. In the following year, 1891, 'Violetta' was figured in that publication, and with many florists it still holds a first place as a bedder. With pollen from 'Violette,' a white-rayed self, still in cultivation, was crossed, which yielded 'Sylvia,' a variety more grown than any Viola yet raised. Of first-rate hardiness, its freedom of flowering is remarkable. By taking 'Violetta' as a seed-bearer, and using pollen from rayless flowers, a great many varieties have been raised, chief among them 'Blue Gown,' 'Florizel,' 'Rosea pallida,' 'Christiana,' 'Coolgardie,' &c. By careful selection the rayless strain of Tufted Pansy has been fixed; and now, if more colours could be got into the flowers, this strain would soon be preferred to the ordinary rayed form. With the fine colours in the Peacock Pansy I was induced to try a cross with the rayless strain. A hundred and fifty plants, the result of the cross, were tested; but the flowers turned out of the most varied character, with one exception, which proved a first-rate departure. A fine reticulated blue; perfectly rayless; and with a good dwarf habit. It was named 'Border Witch,' and is well known as a show flower, and has been certificated. Two years ago Mr. Rowberry, of London, a distinguished amateur, kindly sent me plants and blooms of a yellow self Viola named after himself. The flower was of fine quality, quite rayless, but seemed to have more of the Pansy than Viola in its constitution. This variety, from its fine colour and sturdy constitution, has been the origin of many new forms; but those from 'Mr. Rowberry' have not habits of the dwarfest kind. The pollen from 'Mr. Rowberry' crossed with some of the dwarfest rayless sorts has originated a set of new bedders, which I am convinced in a short time will drive all existing yellow bedders out of the field. 'Coolgardie' x 'Rowberry' has yielded a set of bedders this season varying in shade from orange to paler yellow, which are an immense advance on existing varieties, both in earliness and freedom of flowering. The latter quality comes from 'Mr. Rowberry,' for most of our rayless yellows are by no means early flowerers. Then as to colour, this London variety has furnished several almost orange shades of colour, which are a most desirable attraction. Many seedlings have to be grown before obtaining an orange-coloured Viola, but at present there are several new flowers of this year which answer the description. Among others Messrs. House, of Bristol, have sent out 'Crème d'Orange,' which, during the warm weather in June, has been singularly fine in colour, and could be picked out among hundreds of ordinary yellow varieties. The present taste of the public is for large flowers. 'Mr. Rowberry' will furnish plenty of plants with this desideratum, being a very free seeder. This is not desirable in all cases; as bedding varieties look much better with moderate-sized flowers and plenty of them. The fashion of showing Tufted Pansies in sprays done up with wire is open to criticism; but it seems "the fashion," and we must submit in the meantime. There is just the question whether or no the Tufted Pansy should ever be shown in sprays at all. As a cut flower, the blooms arranged in stalked glasses, garnished with their own foliage, have a good appearance on the table. The Tufted Pansy, however, looks best treated as a perennial in an open situation out of doors with masses of bloom on dwarf plants, where both habit of plant and quality of bloom can be examined. The dwarfer the plants are, with free-flowering properties, the more desirable they are. Take 'Blue Gown' as a type. If every variety had its habit and free-flowering properties we would soon possess a race of Tufted Pansies which would supersede all others. In time this desirable end will be attained.
AQUILEGIA STUARTI.—In May 1880, having plants of Aquilegia glandulosa (Grigor, of Forres, N.B.), as sent out in 1848, also Aquilegia Witmannii, in pots and in flower, at the same time, I fertilised a flower of that species with pollen from A. glandulosa. A ripe pod of seed was gathered in less than a month and sown at once. Seven plants lived, to be planted out on a sheltered border in the autumn. I had almost forgotten their existence, till in the end of May in the following year a floral friend, who was staying here, on looking round before breakfast came on the first open bloom on one of the plants. He asked me where the plant had come from, as the flower was the finest he had seen of the Columbine family. Before referring to my notebook I could hardly tell him, but that they were crossed seedlings I knew quite well. The seven plants all bore flowers identically the same, the top blooms measuring more than four inches across. The following season I took up a quantity of the blooms to a meeting of the Berwickshire Naturalists' Club, and showed them to the late Professor Balfour, of Edinburgh University, and the late Mr. John Sadler, then Curator of the Botanic Gardens, Edinburgh, and many other competent judges, who all considered Aquilegia Stuarti a first-rate novelty, and it was there and then named by Professor Balfour. The original A. glandulosa I have grown on and off for forty years. It is a notoriously shy flowerer, and we used, many years ago, to consider it a triumph to get it to display its beauty at all. All I claim for A. Stuarti is that it is an improved form of A. glandulosa, refined in colour, free flowering, very large and attractive in appearance. It is perfectly hardy, and flowers three weeks before other Columbines, always coming true from seed. It does not, however, succeed in every place, and I know persons who tell me they cannot flower it. After several years' experience in growing and rearing the plant, I recommend that a bed be trenched 2 ft. deep, and well enriched below; the bed raked smooth, and the seed newly ripened, sown thinly in rows, the plants being allowed to remain where they are to flower. The plants, if necessary, may be thinned to a foot between, and the same distance between the rows. In process of time the fine foliage will come to cover the entire bed, and there will be abundance of blooms on moderate sound stems. With a little rotted manure as a top dressing in the autumn, the plants improve in vigour every season, and a three-year-old bed with thousands of blue and white flowers is a sight to see. The specimens sent to the editor of The Garden were taken at random from a bed of the character described, and the beautiful illustration in the number of The Garden, October 18, 1888, was drawn from these specimens.
HYBRID TROLLII.—Everyone is acquainted with our native Trollius europaeus, or Globe Flower, with its beautifully imbricated coloured calm, which it unfolds to the sun and closes at night, the Luckan Gowan of Scotland, and one of our most beautiful native plants. From its symmetrical shape and general hardiness, I thought a cross with the higher coloured American form might yield some improved varieties. A few years ago, with that view, the stamina in an immature state were clipped from some blooms of Trollius europaeus and the flowers marked, and having placed some blooms of T. americanus (?) in a sunny window, I succeeded in getting plenty of pollen, which was applied to the pistils of our native plant. From the complete natural covering of the flower, insects, as a rule, find some difficulty in both entering and getting out of the blooms. Hence when the pollen of T. americanus is dusted over the stigmas, there is less chance of interference. The seeds matured and were sown at once, small, black, shining objects, which if not sown at once refuse to germinate. A goodly array of small plants appeared, and were pricked out into boxes and pans, and ultimately planted in the open ground. They took two seasons to flower; indeed it was the third season before they became good flowering plants. A large proportion of the seedlings showed the effect of the cross, displaying the orange florets of the T. americanus, with improved size of flower and colour in the calyx, all mostly of a vigorous habit of growth. The corollas of the British form never show anything but a pale yellow shade; but when that plant is crossed, most of the seedlings, but not all, demonstrate the influence of the pollen of the other species. The best seedling of the whole, lost from over-kindness, was of a brilliant orange colour, twice the size of T. Fortuni, beautifully imbricated, but seemed delicate in habit. Mrs. Kingsbury, of London, painted it and others; Mr. Dean saw the blooms, and compared them to Orange Roses. During June, 1899, they have bloomed to perfection, in many shades of orange and deep yellow. There remains some doubt as to the pollen bearer being Trollius americanus at all, as a botanist from New York writes me that the American form was a shabby plant and half single. In this instance, however, the pollen bearer happens to be a very handsome form indeed, with bright orange florets, and of robust habit. The Trollius family is among herbaceous plants one of the finest in its season of flowering, and well worth the attention of the hybridist in trying to produce both size of bloom and colour also.
PRIMULAS.—The Primulaceae exhibit an anomaly in their reproductive organs which puzzled many hybridists till the late Mr. Charles Darwin elucidated the cause. He found some Primulae with short stamina and long pistils, and others with long stamina and short pistils. He also, by experiment, proved, in order to get fertile seeds, it was necessary to have pollen from plants with the same length of stamina and pistils. Besides, the size and colour of the pollen grains varied, and was another cause of infertility. The infertility which occurs in various dimorphic and trimorphic plants when illegitimately fertilised, that is, by pollen taken from stamens not corresponding in height with the pistil, differs much in degree, up to absolute and utter sterility, just as in the same manner occurs in crossing distinct species. Florists who have worked to improve the Polyanthus, I mean the Gold-laced show variety, must all have observed the great difficulty of obtaining good fertile seed. When the stamina occupy the centre of the flower or corolla, florists denominate the condition as thrum-eyed, and is the true form, other things being equal. When the pistil protrudes in the centre, then "pin-eyed" is the name applied. It is no use to apply pollen from a short-stamened flower to the protruding pistil of the pin-eyed flower, but with pollen from a long-stamened flower a cross can be obtained that will produce good flowers from fertilised seed. This is exactly how florists work in obtaining new varieties. A pin-eyed flower of fine lacing and trussing habit is chosen for the seed bearer. The pistil is dusted with pollen from a good show flower, which must be thrum-eyed and with long stamina; and, other things being favourable, good reliable seed is the result. No flower has given worse produce than the show Polyanthus, simply from the fact of the ignorance of the raisers, till Mr. Charles Darwin proved by his own experiments the reason why, and solved the problem. In following out his theories and practice, I have during the last few years tried to get the bright colour of some of our Alpine Auriculas infused into the Primula Auricula of the Alps and mountains of the Tyrol; and I do not despair of getting the hardy free-growing Primula marginata, with its beautiful foliage, to reciprocate a cross with the pollen from some of their high-coloured relations. As it is, P. viscosa, P. integrifolia, and P. ciliata have already furnished me with encouraging results, which in another season I hope to improve upon. The weather during the spring has been so cold, sunless, and wet that little could be done in the way of crossing the varieties of Primula. Although the plants are kept in the meantime in rudely constructed cold frames, very little seed will be got. Careful testing of seedlings already obtained is just as important, and I hope next season to have something to show. There is a vigour of constitution in these crossed seedlings which contrasts favourably with that of the old show varieties of Auricula, which owing to lack of constitution are now only grown by some enthusiasts, beautiful though they undoubtedly are.